The size of the pelvis during pregnancy is measured during the first visits to the doctor’s office. Such parameters are studied in order to determine the future course of labor, as well as to diagnose possible asymmetry or abnormal structure.
General information about the structure of the pelvis
The hip apparatus is formed by the sacrum, coccyx and two pelvic bones, which are connected to each other using ligaments and cartilage. The main difference between the structure of women's hips and men's is that it is wider and more voluminous. This state of affairs is explained by the reproductive function, since it is here, in the uterine cavity, that the embryo will grow and develop, and subsequently the movement of the formed fetus will begin along the birth canal.Normal natural delivery depends on the structure and size. Violation of symmetry, deviations and anomalies often lead to complications during pregnancy and childbirth. Measurements become especially important if an ultrasound reveals the baby is presenting, then maximum care will be required on the part of doctors.
Normal pelvic sizes in obstetrics during pregnancy
Measuring the pelvis during pregnancy is used at least twice, at the first visits to the doctor and for more later. The study is carried out both by palpation and using a special pelvic meter device. The dimensions of the pelvis during pregnancy make it possible to assess a woman’s capabilities before childbirth, whether medical intervention will be required or whether the pregnant woman is able to give birth to a child on her own without serious consequences.First, doctors need to measure the Michaelis rhombus, or lumbosacral rhombus, which is assessed while standing at the back of the sacrum and should be symmetrical in shape. In normal condition, the vertical length is 11 cm and the width is 10 cm. Any deviations, non-standard form and a fuzzy diamond-shaped silhouette indicate that difficulties arise as pregnancy progresses.
- interosseous measurement of about 25-26 centimeters - determines the distance between the most protruding points of the bone in front;
- between the crests of the iliac bone tissues the distance should be 28-29 cm - this is the norm;
- the length between the greater trochanters of the 2 femurs is 30-32 centimeters.
Table of normal values for pelvic size during pregnancy:
The interpretation of the latest measurements is carried out by the doctor by subtracting 9 centimeters from the external parameters. But, in some situations, it is necessary to measure the circumference of a woman’s wrist in order to understand the width of the bone. Thus, if the wrist diameter exceeds 15 cm, then 10 cm must be subtracted.
It should be remembered that the difference between the first three measurements is on average 3 cm; a decrease in this value suggests a significant narrowing of the pelvic bones.
The importance of a wide and narrow pelvis during pregnancy
When the measurement values are greater than normal, it becomes clear that the pregnant woman has wide pelvis, this is physiological norm and does not pose a danger to the child. In rare cases, wide parameters may indicate the rapidity of labor, which is fraught with ruptures in the perineum.A narrow pelvis is diagnosed when the parameters decrease from 1.5 cm. At the same time, in obstetrics there is the concept of anatomical narrowing, which is observed when the norm decreases to 2 cm. Diagnosing a narrowing does not necessarily indicate a pathologically difficult birth. Often women with narrow parameters give birth to a small baby, and the head passes without difficulty. The indicator is measured to assess risks; if a large fetus develops inside the womb, this often leads to serious consequences during the process of natural spontaneous childbirth.
Narrow pelvis - risk factors for pregnant women
Adverse consequences due to a lower hip ratio are possible not only at the stage of delivery, but also in late pregnancy. So, when the baby’s head drops lower to the pelvis, the uterus rises accordingly, this hinders the respiratory activity of the body, and significant shortness of breath appears.According to statistics, pregnant women with narrow hips are much more likely to be diagnosed with fetal presentation. Therefore, they belong to a group that requires careful monitoring by medical specialists in order to reduce the likelihood of complications during the birth of the baby. Early effusion is not uncommon amniotic fluid, hypoxia and loss of some parts (umbilical cord, arms, legs) during pushing.
Post-term pregnancy is considered the most dangerous if narrow hips are diagnosed. Often, doctors decide to perform a planned caesarean section in order to minimize the risk of serious injury.
The examination plan for a pregnant woman must include measuring the pelvis. This procedure is often performed at the first appointment for every woman who consults an obstetrician-gynecologist about the desired pregnancy. Bone pelvis and soft fabrics lining it are the birth canal through which the baby is born. It is extremely important for doctors and women to know whether the birth canal is too small for the baby. This circumstance determines the possibility of childbirth through the natural birth canal. The results of the pelvic examination are included in the medical records. So that you can understand what is written on your exchange card, we will talk in detail about what the doctor does when measuring a pregnant woman’s pelvis.
Measuring the pelvis during pregnancy
The structure and size of the pelvis are crucial for the course and outcome of childbirth. Deviations in the structure of the pelvis, especially a decrease in its size, complicate the course of labor or present insurmountable obstacles to it.
The pelvis is examined by inspection, palpation and measurement. During the examination, attention is paid to the entire pelvic area, but special importance is attached to the sacral rhombus (Michaelis rhombus, Fig. 1), the shape of which, together with other data, allows us to judge the structure of the pelvis (Fig. 2).
Rice. 1. Sacral rhombus,or Michaelis rhombus
Rice . 2. Bonespelvis
Most important of all methods of pelvic examination has its measurement. Knowing the size of the pelvis, one can judge the course of labor, the possible complications with them, about the admissibility of spontaneous childbirth with a given shape and size of the pelvis. Most of the internal dimensions of the pelvis are not available for measurement, so the external dimensions of the pelvis are usually measured and the size and shape of the small pelvis can be approximately judged from them. The pelvis is measured with a special instrument - a pelvic meter. The pelvis meter has the shape of a compass equipped with a scale on which centimeter and half-centimeter divisions are marked. There are buttons at the ends of the branches of the tazomer; they are applied to places the distance between which is to be measured.
Usually measured following sizes pelvis: (Latin names and abbreviations are indicated in parentheses, since the dimensions are indicated that way in the exchange card.)
Distance spinarum (DistantiasplnarumD.sp.)- the distance between the anterior superior iliac spines. This size is usually 25-26 cm (Fig. 3).
Rice. 3. Measuring spinarum distance
Distance cristarum (Distantiacristarum D. Cr.)- the distance between the most distant points of the iliac crests. It averages 28-29 cm (Fig. 4).
Rice. 4. Crystarum distance measurement
Triangular distance (Distantiatrochanterica D. Tr.)- the distance between the greater trochanters of the femurs. This size is 31 -32 cm (Fig. 5).
Rice. 5. Measuring the distance of the triangular
Conjugata externaС. Ext.- external conjugate, i.e. straight pelvic size. To do this, the woman is laid on her side, the underlying leg is bent at the hip and knee joints, and the overlying leg is extended. The outer conjugate is normally 20-21 cm (Fig. 6).
Rice. 6. Measuring the outer conjugate
External conjugate is important: by its size one can judge the size true conjugates- the distance between the sacral promontory - the most protruding point inside the sacrum and the most protruding point on the inner surface of the pubic symphysis (the junction of the pubic bones). This smallest size inside the pelvis through which the fetal head passes during childbirth. If the true conjugate is less than 10.5 cm, then vaginal delivery may be difficult or simply impossible; in this case, a caesarean section is often performed. To determine the true conjugate, subtract 9 cm from the length of the outer conjugate. For example, if the outer conjugate is 20 cm, then the true conjugate is 11 cm; if the outer conjugate has a length of 18 cm, then the true one is 9 cm, etc. The difference between the external and true conjugates depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of bones and soft tissues varies in women, so the difference between the size of the external and true conjugate does not always exactly correspond to 9 cm. The true conjugate can be more accurately determined by the diagonal conjugate.
Diagonal conjugate (conju-gatadiagonalis) is the distance from the lower edge of the symphysis to the most prominent point of the sacral promontory. The diagonal conjugate is determined during a vaginal examination of the woman (Fig. 7). The diagonal conjugate with a normal pelvis is on average 12.5-13 cm. To determine the true conjugate, 1.5-2 cm is subtracted from the size of the diagonal conjugate.
Rice. 7. Diagonal conjugate measurement
The doctor is not always able to measure the diagonal conjugate, because with normal pelvic sizes during a vaginal examination, the promontory of the sacrum is not reached by the examiner’s finger or is difficult to palpate. If during a vaginal examination the doctor does not reach the promontory, the volume of this pelvis can be considered normal. The dimensions of the pelvis and the external conjugate are measured in all pregnant women and women in labor without exception.
If during examination of a woman there is a suspicion of narrowing of the pelvic outlet, then the size of this cavity is determined. These measurements are not mandatory, and are measured in a position in which the woman lies on her back, legs bent at the hip and knee joints, spread to the side and pulled up to the stomach.
Determining the shape of the pubic angle is important. With normal pelvic sizes it is 90-100°. The shape of the pubic angle is determined by the following technique. The woman lies on her back, legs bent and pulled up to her stomach. Palm side thumbs applied close to the lower edge of the symphysis. The location of the fingers allows us to judge the angle of the pubic arch.
Additional Research
If it is necessary to obtain additional data on the size of the pelvis, its correspondence to the size of the fetal head, deformations of the bones and their joints, an X-ray examination of the pelvis is performed - X-ray pelviometry. Such an examination is possible at the end of the third trimester of pregnancy, when all the organs and tissues of the fetus are formed and an x-ray examination will not harm the baby. This study is carried out with the woman lying on her back and side, which makes it possible to determine the shape of the sacrum, pubic and other bones; A special ruler is used to determine the transverse and straight dimensions of the pelvis. The fetal head is also measured, and on this basis it is judged whether its size corresponds to the size of the pelvis.
The size of the pelvis and its correspondence to the size of the head can be judged from the results ultrasound examination. This study allows you to measure the size of the fetal head, determine how the fetal head is located, because in cases where the head is extended, that is, the forehead or face is presented, it requires more space than in cases where the occiput is presented. Fortunately, in most cases, birth takes place in the occipital presentation.
When measuring externally, it is difficult to take into account the thickness of the pelvic bones. Measuring the circumference of the wrist joint of a pregnant woman with a centimeter tape is of known importance. (Soloviev index). The average value of this circumference is 14 cm. If the index is larger, it can be assumed that the bones of the pelvis are massive and the dimensions of its cavity are smaller than would be expected from measurements of a large pelvis. If the index is less than 14 cm, then we can say that the bones are thin, which means that even with small external dimensions, the dimensions of the internal cavities are sufficient for the baby to pass through them.
Long gone are the days when a narrow pelvis was a kind of death sentence for a woman in labor. Modern medicine makes it possible to ensure a successful outcome of childbirth, regardless of the structural features of the woman’s pelvis. But for this, doctors must carry out the necessary measurements in a timely manner. And every woman should be aware of the significance of this procedure.
Details
Pelvic dimensions are of key importance in obstetrics: they determine the possibility and expected mechanism of childbirth, are necessary for choosing labor management tactics, and indications for a Caesarean section.
Wire axis= midpoints of straight dimensions
Anatomical conjugate– from the middle of the upper edge of the pubic arch to the most prominent point of the promontory = true conjugate+ 0.2-0.3 cm
(Table with scroll bar. On mobile devices, move the table by tapping on the screen)
|
Pelvic plane |
Landmarks |
Dimensions (cm) |
|||||
|
Straight (cm) |
Transverse (cm) |
Oblique (cm) |
|||||
|
Login |
Upper inner edge of the pubic arch, innominate lines, tip of the sacral promontory |
the middle of the upper inner edge of the pubic arch is the most prominent point of the promontory = true conjugate |
13,5 |
between the most distant points of unnamed lines |
right - from the right sacroiliac joint to the left iliopubic tubercle, left - vice versa) |
||
|
Wide part |
The middle of the inner surface of the pubic arch, the middle of the smooth plates, the articulation between II and III sacral vertebrae |
12,5 |
the middle of the inner surface of the pubic arch is the articulation between II and III sacral vertebrae |
12,5 |
between the most distant points of the acetabulum |
||
|
Narrow part |
Lower edge of the symphysis pubis, ischia, sacrococcygeal joint |
11,5 |
lower edge of the pubic arch – sacrococcygeal joint |
10,5 |
between the inner surfaces of the ischial spines |
||
|
Exit |
The lower edge of the pubic arch, the inner surfaces of the ischial tuberosities, the apex of the coccyx (two planes converging at an angle along the line connecting the ischial tuberosities) |
9,5 (11,5) |
the middle of the lower edge of the symphysis pubis - the tip of the coccyx |
between the most distant points of the internal surfaces of the ischial tuberosities |
|||
True conjugate.
True, or obstetric, conjugate(conjugata vera, s. obstetrica) is called shortest distance between the promontory and the point most prominent into the pelvic cavity on the inner surface of the symphysis. Normally this distance is 11 cm.
Exists four main ways to determine the value of conjugata vera.
According to the size of the outer conjugate. For example, with an external conjugate of 20 cm and a Solovyov index of 1.2, it is necessary to subtract 8 cm from 20 cm, and we obtain a true conjugate of 12 cm; with a Solovyov index of 1.4, you need to subtract 9 cm from 20 cm; with a Solovyov index of 1.6, 10 cm must be subtracted, the true conjugate will be equal to 10 cm, etc.
According to the size of the diagonal conjugates. To do this, the Solovyov index is subtracted from the length of the diagonal conjugate. For example, subtracting the Solovyov index of 1.4 from the size of the diagonal conjugate (10.5 cm), we obtain a true conjugate of 9.1 cm (I degree of pelvic narrowing), and subtracting 1.6 - 8.9 cm (II degree of pelvic narrowing).
According to the vertical size of the Michaelis rhombus (distantia Tridondani). The vertical size of the rhombus corresponds to the size of the true conjugate.
According to the value of the Frank index (distance from the incisura jugularis to the spinous process of the VII cervical vertebra). This size corresponds to the size of a true conjugate.
External conjugate. To determine the true conjugate, subtract 9 cm from the length of the outer conjugate. For example, if the outer conjugate is 20 cm, then the true conjugate is 11 cm; if the outer conjugate has a length of 18 cm, then the true one is 9 cm, etc.
The difference between the external and true conjugate depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of bones and soft tissues varies in women, so the difference between the size of the external and true conjugate does not always exactly correspond to 9 cm. The true conjugate can be more accurately determined by the diagonal conjugate.
Diagonal conjugate(conjugata diagonalis) is the distance from the lower edge of the symphysis to the most prominent point of the promontory of the sacrum. The diagonal conjugate is determined during a vaginal examination of a woman, which is performed in compliance with all the rules of asepsis and antiseptics. The II and III fingers are inserted into the vagina, the IV and V are bent, their back rests against the perineum. The fingers inserted into the vagina are fixed at the top of the promontory, and the edge of the palm rests against the lower edge of the symphysis. After this, the second finger of the other hand marks the place of contact of the examining hand with the lower edge of the symphysis. Without removing the second finger from the intended point, the hand in the vagina is removed, and the assistant measures the distance from the top of the third finger to the point in contact with the lower edge of the symphysis with a pelvis or a centimeter tape.
A narrow pelvis is considered one of the most complex and difficult sections of obstetrics, since this pathology can lead to the development of dangerous complications during childbirth, especially if they are performed incorrectly. According to statistics, anatomical narrowing of the pelvic bones occurs in 1-7.7% of cases, while during childbirth such a pelvis becomes clinically narrow in 30%. If we take the total number of all births, then this pathology accounts for about 1.7% of cases.
The concept of “narrow pelvis”
During the period when the fetus is expelled from the uterus or during the pushing period, the child must overcome the bone ring that is formed by the pelvic bones. This ring consists of 4 bones: the coccyx, the sacrum and two pelvic bones, which are formed by the ischium, pubis and ilium. These bones are connected to each other using ligaments and cartilage. The female pelvis, unlike the male one, is larger and wider, but has less depth. A pelvis with normal parameters plays an important role in the normal, physiological course of childbirth without complications. If there are deviations in the symmetry and configuration of the pelvis, its size decreases, then the bony pelvis serves as a kind of obstacle to the passage of the fetal head.
In practical terms, two types of narrow pelvis are classified:
a clinically narrow pelvis occurs in the event of a discrepancy between the anatomical dimensions of the woman’s pelvis and the dimensions of the child’s head during childbirth (however, even in the presence of an anatomical narrowing of the pelvis during childbirth, a functionally narrow pelvis may not always occur, for example, when the fetus is small in size, or vice versa, when functional pelvic indicators are normal, but the large size of the baby leads to the development of a clinically narrow pelvis);
An anatomically narrow pelvis is characterized by a narrowing of several or one size by 2 or more centimeters.
Causes
The causes of a narrow pelvis are different - in the event of a disproportion between the parameters of the mother’s pelvic bones and the baby’s head or in the presence of an anatomical narrowing.
Etiology of anatomically narrowed pelvis
The following factors can provoke the occurrence of an anatomically narrowed pelvis:
heavy physical labor and malnutrition in childhood;
frequent colds, as well as increased physical activity in adolescence;
neuroendocrine pathologies;
late onset of menstruation, impaired fertility, disruptions in menstrual function.
Anatomical narrowing of the pelvis occurs due to the following reasons:
delayed sexual development;
infantilism, both sexual and general.
dislocations of the hip joints;
excess androgens, hyper- and hypoestrogenism;
impaired mineral metabolism;
practicing professional sports (swimming, gymnastics, licking);
psycho-emotional stress and stressful situations that provoke the occurrence of “compensatory hyperfunction of the body”, as a result of which a transversely narrowed pelvis is formed;
acceleration (rapid growth of the body in length against the background of a slow increase in transverse pelvic parameters);
damaging factors that affected the fetus in the antenatal period;
tumors and exostoses of the pelvis;
polio;
heredity and constitutional features;
cerebral palsy;
curvature of the spine (coccyx fractures, scoliosis, kyphosis, lordosis);
pelvic bone fractures;
bone tumors, bone tuberculosis, osteomalacia;
Etiology of a functionally narrow pelvis
Disproportion between the mother's pelvis and the baby's head during childbirth is caused by:
preposition with the pelvic end;
atresia (narrowing) of the vagina;
neoplasms of the ovaries and uterus;
pathological insertion of the head (frontal insertions, asynclitism);
malposition;
difficulty in the process of configuration of the bones of the baby’s skull (in case of true postmaturity);
large weight and size of the fetus;
anatomical narrowing of the pelvis.
Childbirth, which is complicated by a clinically narrow pelvis, ends with a cesarean section in 9-50% of cases.
Narrow pelvis: varieties
There are many classifications of anatomically narrowed pelvis. Quite often in the obstetric literature a classification is presented that is based on morphological and radiological characteristics:
Gynecoid type
It makes up about 55% of the total number of pelvises and is a normal type of female pelvis. Body type of the expectant mother female type, thin waist and neck, hips are wide, height and weight are within the average range.
Android pelvis
Is the pelvis male type and occurs in 20% of cases. The woman has a masculine physique, namely an undefined waist, a thick neck against the backdrop of narrow hips and broad shoulders.
Anthropoid pelvis
It is characteristic of primates and accounts for about 22% of cases. This form is distinguished by an increase in the direct size of the entrance, which significantly exceeds the transverse size. Women with this pelvic configuration are tall, lean, their shoulders are quite wide, while their hips and waist are narrow, their legs are thin and elongated.
Platypeloid pelvis
Its shape resembles a flat pelvis and occurs in 3% of women. A woman with such a pelvis is tall, markedly thin, has reduced skin elasticity and underdeveloped muscles.
Narrowed pelvis: forms
Classification of a narrow pelvis according to Krassovsky:
Common forms:
pelvis with a reduced wide part of the pelvic cavity;
flat-rachitic;
simple flat (Deventrovsky).
transversely narrowed pelvis (Robertovsky);
generally uniformly narrowed pelvis (ORST) is the most common type, which is observed in 40-50% of the total number of pelvises;
flat pelvis, occurs in 37% of cases, is divided into:
Rare forms:
assimilation;
osteomalatic;
spondylolisthetic form;
kyphotic form;
funnel-shaped;
generally narrowed flat.
pelvic deformation by fractures, exostoses, bone tumors;
obliquely contracted and obliquely displaced;
other forms:
Degrees of narrowing
The classification proposed by Palmov is based on the degree of narrowing of the pelvis:
first degree – less than 11 cm, not shorter than 9 cm;
second degree - true conjugate indicators from 9 to 7.5 cm;
third degree – the length of the true conjugate is from 7.5 to 6.5 cm;
fourth degree – absolutely narrow pelvis, shorter than 6.5 cm.
first degree - the transverse diameter of the entrance to the pelvis is within 12.4-11.5 cm;
second degree - transverse diameter of the entrance - 11.4-10.5 cm;
third degree - the transverse diameter of the entrance to the small pelvis is shorter than 10.5 cm.
first degree – diameter is 12.4-11.5 cm;
second degree – diameter less than 11.5 cm.
along the length of the true conjugate (normally 11 cm) refers to the flat pelvis and ORST:
according to the parameter of the transverse diameter of the pelvic inlet (the norm is 12.5-13 cm), it refers to a transversely narrowed pelvis:
in terms of the diameter of the wide part of the pelvic cavity (norm 12.5 cm):
Dimensions of anatomically narrowed pelvis of various shapes
Narrow pelvis: size table in centimeters
|
Pelvic shape |
|||||
|
Simple flat |
flat-rachitic |
transversely narrowed |
normal |
||
|
external |
25/26-28/29-30/31 |
||||
|
External conjugate |
|||||
|
Diagonal conjugate |
|||||
|
True conjugate |
|||||
|
Michaelis rhombus |
|||||
|
Vertical diagonal |
|||||
|
Horizontal diagonal |
|||||
|
Entrance plane |
|||||
|
Lateral conjugate |
|||||
|
Transverse |
|||||
|
Differential criterion |
Reducing direct dimensions in all planes |
Reducing the direct size of the pelvic inlet plane |
Uniform decrease in parameters (all) by 1.5 cm |
Shortening transverse dimensions |
None |
Diagnostics
A narrowed pelvis is diagnosed and assessed under conditions antenatal clinic, on the day of registration of a pregnant woman. To determine a narrow pelvis during pregnancy, the doctor must study the anamnesis, perform an objective examination, including vaginal examination, pelvic measurement, palpation of the uterus and pelvic bones, body examination, anthropometry. If necessary, additional research methods may be prescribed: ultrasound scanning and X-ray pelviometry.
Anamnesis
It is important to pay attention and study the living conditions and illnesses of a pregnant woman in childhood (chronic pathology and injuries, intense stress in sports, hard physical work and poor nutrition, hormonal imbalance, bone tuberculosis and osteomyelitis, polio and rickets). Obstetric history data are also important:
whether there was stillbirth or death of the newborn in the neonatal period;
for what reason was surgical delivery performed, whether there were traumatic brain injuries in the fetus during childbirth;
how the previous births proceeded.
Objective research
Anthropometry
Low height (less than 145 cm) in most cases indicates the presence of a narrowed pelvis. However, it is possible for tall women to have a transversely narrowed pelvis.
Assessment: silhouette, build, gait
It has been proven that in the presence of a strongly protruding belly forward, the center of the upper body shifts posteriorly, to maintain balance, the lower back moves forward, increasing lumbar lordosis, as well as the angle of inclination of the pelvis.
Abdominal shape assessment
It is known that primigravida women have an elastic abdominal anterior wall, as a result of which the abdomen acquires a pointed shape. Multiparous women have a saggy abdomen, since the head at the end of the gestation period is not inserted into the entrance of the pelvis (narrowed), while the uterine fundus is high, and the uterus itself has a deviation anteriorly and upwardly from the hypochondrium.
Palpation of the Michaelis diamond and inspection.
Identification of signs of virilization and sexual infantilism.
The Michaelis rhombus is formed by the following anatomical formations:
on the sides - the upper posterior projections (or spines) of the ilium;
below – the apex of the sacrum;
above – the lower border of the fifth lumbar vertebra.
Pelvic palpation
During palpation of the iliac bones, their location, contours and slope are determined. During palpation of the trochanters (greater trochanters of the femurs), it is possible to determine the presence of an obliquely displaced pelvis if the trochanters are located at different levels and are deformed.
Vaginal examination
Allows you to determine the capacity of the pelvis, evaluate the shape and examine the sacrum, the presence of bony protrusions, and the depth of the sacral cavity. It is also possible to determine the deformation of the lateral walls of the pelvis, determine the diagonal conjugate and the height of the symphysis.
Pelvis measurement
Basic measurements:
the uterus is measured to determine the approximate weight of the fetus;
the height of the pubic symphysis is set;
the pubic angle is determined (the norm is 90 degrees);
measuring the pubosacral size (measure the segment from the junction of the second and third sacral vertebrae to the middle of the symphysis). Normal is 21.8 cm;
Solovyov index – measurement of the wrist circumference at the level of the forearm condyles. Using this index, the thickness of the bones is determined: a small index is responsible for thin bones, and a large index for thick bones, respectively. The norm is 14.5 - 15 centimeters;
Michaelis rhombus measurement (horizontal diagonal 10 cm, vertical diagonal 11 cm). The presence of diamond asymmetry indicates curvature of the spinal column or pelvis;
external conjugate - measuring the distance from the upper edge of the womb to the upper corner of the Michaelis rhombus. Normal is 20 centimeters;
Distantia trohanterica - the segment between the two trochanters of the femur, normally 31-32 centimeters;
Distantia cristarum - the segment between the most distant points of the iliac crests. Normally – 28-29 centimeters;
Distantia spinarum - the segment between the upper anterior projections of the ilium. Normal is 25-26 centimeters.
Additional measurements:
if pelvic asymmetry is suspected, the lateral Kerner conjugate and oblique dimensions are determined;
measure the pelvic outlet;
measure the angle of inclination of the pelvis.
Special research methods
X-ray pelviometry
X-ray examinations are allowed only during childbirth or after the 37th week of pregnancy. With its help, the nature of the structure of the pelvic walls, the size and shape of the pubic arch, the severity of the sacral curvature, the features of the ischial bones are determined; this method also allows you to determine all the diameters of the pelvis, the size of the fetal head and its position relative to the pelvic planes, the presence of fractures and tumors.
Ultrasound
Allows you to determine the size of the head and its location, the true conjugate, and evaluate the features of insertion of the fetal head into the entrance. Using a transvaginal sensor, you can set all the necessary pelvic diameters.
Method for calculating true conjugates
For this purpose, the following methods are used:
on ultrasound examination of the pelvis;
according to X-ray pelviometry;
according to the Michaelis diamond: the upper size of the diamond corresponds to the conjugate (true) indicator;
1.5-2 centimeters are subtracted from the diagonal conjugate index (if the Solovyov index is 14-16 cm or less, 1.5 cm is subtracted, if the Solovyov index exceeds 16 cm, then 2 cm is subtracted);
subtract 9 from the size of the external conjugate (the norm is at least 11 cm).
Features of pregnancy
In the first half of the gestation period, complications in the presence of a narrowed pelvis are not observed. However, the nature of the course of pregnancy in the second half is aggravated by the influence of the underlying pathology, which led to the formation of a narrow pelvis, while complications (intrauterine infection, gestosis) and extragenital pathologies have a certain influence. For pregnant women with a narrow pelvis it is typical:
high position of the head against the background of the inability to insert it into the pelvis. This is due to the high position of the diaphragm and uterine fundus, causing increased heart rate, fatigue and shortness of breath;
quite often pregnancy can be complicated by premature rupture amniotic fluid, due to lack of contact with the pelvic inlet due to the high position of the head;
significant fetal mobility can cause extensor or breech presentation And incorrect position fetus;
the risk of premature birth increases;
the formation of a saggy abdomen in multiparous women and a pointed abdomen in primiparous women can provoke asynclitic insertion of the head during labor.
Pregnancy management
All pregnant women with a narrow pelvis are placed on a special register with an obstetrician. A few weeks before the onset of labor, a woman must be routinely hospitalized in the antenatal department. Here the gestational age is specified, and calculations are also performed estimated weight of the fetus, measure the pelvis, clarify the presentation of the fetus and its condition, and, based on the data obtained, select the most suitable option delivery (form a plan for the management of childbirth).
The method of delivery is selected based on medical history, the degree and form of anatomical narrowing of the pelvis, the approximate weight of the child, as well as other complications of pregnancy. Natural childbirth can be carried out in the case of prematurity, first degree contraction with a mature cervix and normal fetal size, in the absence of an aggravating medical history.
Planned surgical delivery (caesarean section) is performed if the following indications exist:
3-4 degree of narrowing of the pelvis (very rare);
a combination of any obstetric pathology requiring a cesarean section and a narrow pelvis;
birth of a fetus with birth trauma, complications in previous births, history of stillbirth, older women in labor;
a combination of the first or second degree of contraction with the presence of a large fetus, post-term pregnancy, abnormal position of the child, breech presentation.
Pregnancy and pain in the pelvic bones
Pain in the pelvic bones begins to appear after 20 weeks and can be caused by various reasons:
Calcium deficiency
Aching constant pain that is not associated with changes in body position or movement. It is recommended to take vitamin D in combination with calcium supplements.
Separation of the pelvic bones and sprain of the uterine ligaments
How larger size uterus, the more intense the tension is experienced by the uterine ligaments that hold it, this manifests itself in discomfort and pain while walking, as well as when the child moves. The provocateurs of the process are relaxin and prolactin, under the influence of which the pelvic cartilage and ligaments swell and soften in order to facilitate the passage of the fetus through the bone ring. To relieve such pain, it is recommended to wear a bandage.
Divergence of the symphysis pubis
Excessive swelling of the symphysis, which is a rather rare pathology, is accompanied by bursting pain in the pubic area, and it also becomes impossible to raise the leg while in a horizontal position. This pathology is called symphysitis, it is accompanied by divergence of the symphysis pubis. Treatment through surgery after delivery is effective.
Course of labor
Today, the tactics of labor management in the presence of a narrow pelvis imply a significant increase in the indications for performing abdominal delivery, both planned and emergency, in the presence of complications during childbirth. Natural childbirth is a very difficult task, since the outcome can be either favorable or unfavorable for both the child and the woman. If there is a third and fourth degree of narrowing, the birth of a full-term live child is impossible - only a planned operation. If there is a narrowing of the pelvis to the first or second degree, a successful outcome natural birth depends on the parameters of the fetal head, its ability to configure, the nature of insertion and the intensity of the labor activity.
Complications during childbirth in the presence of a narrow pelvis
First period
During the opening of the uterine pharynx, the following complication of childbirth may occur:
oxygen starvation of the fetus;
loss of small parts or loops of the baby’s umbilical cord;
early rupture of amniotic fluid;
weakness of labor forces (in 10-38% of cases).
Second period
During the expulsion of the fetus through the birth canal, the following complications may occur:
damage to the nerve plexuses of the pelvis;
damage to the symphysis pubis;
necrosis (death) of tissues of the birth canal with subsequent formation of fistulas;
birth injury;
threat of uterine rupture;
intrauterine hypoxia;
development of secondary weakness of generic forces.
Third period
In the last stage of labor, as well as in the early postpartum period, bleeding may occur, which occurs due to a long anhydrous interval and the course of labor.
Management of childbirth
Today, the most correct tactics for managing childbirth in the presence of such a pathology is active expectant tactics. At the same time, the tactics for conducting the birth process should be purely individual and based not only on the degree of narrowing of the pelvis and the results of an objective study expectant mother, but also on the prognosis for the child and woman. The birth plan should have the following points:
fetal destruction surgery intrauterine death fetus;
performing a cesarean section when the fetus is alive and there are indications for surgery;
preventive measures in the afterbirth and early postpartum periods;
identifying signs of clinical inconsistency;
prevention of infectious complications;
prevention of intrauterine starvation of a child;
prevention of the development of weakness of generic forces;
bed rest during labor, which can prevent early release of water (the woman should be on the side to which the baby’s back is adjacent).
During childbirth, monitoring of discharge from the genital tract (bloody, leakage of water, mucous), urination, and the condition of the vulva (presence of swelling) is carried out. If urinary retention is present, catheterization is performed. Bladder, however, it should be remembered that such a sign may indicate a disproportion between the baby’s head and the pelvic dimensions of the woman in labor.
The most common complication during childbirth in the presence of a narrowed pelvis is premature rupture of amniotic fluid. If there is an “immature” cervix, surgical delivery is required. With a “mature” cervix, labor-inducing manipulations are indicated (provided that the child’s weight does not exceed 3.6 kg and the first degree of narrowing is present).
During the period of contractions, in order to prevent their weakness, it is necessary to create an energy background; the woman in labor receives medicated sleep and rest in a timely manner. When assessing the effectiveness of labor, the obstetrician must monitor not only the dynamics of cervical dilatation, but also the nature of the movement of the head along the birth canal.
Induction of labor should be performed carefully, and its duration cannot exceed 3 hours (if there is no effect, a caesarean section). In addition, in the first stage of labor, antispasmodics must be administered (with an interval of 4 hours), Nikolaev’s triad is performed to prevent hypoxia, and antibiotics are prescribed as the anhydrous period increases.
The period of expulsion may be complicated by secondary weakness, the development of fetal hypoxia, and if the fetal head remains in the birth canal for a long time, fistulas may form. Therefore, timely emptying of the bladder and episiotomy are required.
Disproportions between the mother's pelvis and the baby's head
The occurrence of a clinically narrow pelvis is promoted by:
abnormal forms of a narrow pelvis;
a large head of the child in the presence of normal pelvic sizes;
incorrect presentation of the fetus or unsuccessful insertion of the head;
large fetus and slight narrowing of the pelvis.
During childbirth, a functional assessment of the pelvis must be performed, which consists of:
in identifying signs of Zangheimester and Vasten (after the discharge of amniotic fluid);
in the diagnosis of a generic tumor of the soft tissues of the head, the rate of its growth and appearance;
assessing the configuration of the child’s head;
in determining the characteristics of the insertion and subsequent assessment of the biomechanism of labor based on insertion data.
Signs of a clinically narrow pelvis:
premature and early rupture of water;
significant head configuration;
protracted course of 1st period;
the emergence of a clinical threat of uterine rupture;
positive signs according to Zangheimester, Vasten;
symptoms of compression of the bladder and soft tissues (blood in the urine, urinary retention, swelling of the vulva and cervix);
the occurrence of attempts when the fetal head is pressed to the entrance to the pelvis;
the head does not move forward when the contractions are strong enough, the water breaks and the uterine os is fully opened;
the biomechanism of labor is disrupted and does not correspond to this type of pelvic narrowing.
Vasten's sign is determined by palpation (the relationship between the inlet of the pelvis and the baby's head is determined). A negative sign of Vasten is a condition in which the head is inserted into the pelvis, located below the pubic symphysis (the obstetrician’s palm drops below the pubis). Level symptom – the doctor’s palm is located at the level of the womb (the symphysis and the head are in the same plane). A positive sign is that the obstetrician’s palm is located higher from the symphysis (the head is located above the plane of the pubis).
If a negative sign is present, labor ends on its own (since the sizes of the pelvis and head correspond). If the symptom is level, with an adequate configuration of the head and effective labor, labor is also independent. If the sign is positive, spontaneous childbirth is excluded.
Kalganova proposed using three degrees of discrepancy between the head and pelvic dimensions:
First degree, or relative non-conformity.
There is correct head insertion and adequate configuration. The contractions are of sufficient strength and duration, but the advancement of the head and the opening of the uterus are slowed down, in addition, the discharge of water is untimely. Urination is difficult, but Vasten's sign is negative. Another option is to complete the labor on your own.
Second degree, or significant discrepancy.
The insertion of the head and the biomechanism of labor are not normal; the head has a sharp configuration and remains in the same plane for a long time. Urinary retention and abnormalities in labor (weakness or incoordination) appear. Westen's sign - level.
Third degree, or absolute inconsistency.
Attempts occur prematurely against the background of a complete lack of advancement of the head, even despite complete opening and good contractions. The birth tumor grows rapidly, signs of compression of the bladder appear, and there is a threat of uterine rupture. Westen's sign is positive.
The presence of second and third degrees of discrepancy is an indication for immediate surgical delivery.
Case Study
A woman with her first birth (20 years old) was admitted to the maternity hospital complaining of contractions for two hours. There was no outpouring of water. The general condition of the woman in labor is satisfactory, pelvic dimensions: 24.5-26-29-20, abdominal circumference - 103 centimeters, height of the uterine fundus - 39 centimeters. The position of the fetus is longitudinal, the head is pressed to the entrance to the pelvis. Auscultation: no pain, heartbeat is clear. Contractions are of good duration and strength. Approximate weight fruit 4 kg.
During a vaginal examination, it was determined: the cervical dilatation is 4 cm, has stretchable thin edges, and is smoothed. The amniotic sac is functioning normally, the fluid is intact. The head is pressed, the cape is not accessible. Diagnosis: 38 weeks pregnancy, first stage of first full term birth. Transversely narrowed pelvis of the first degree, the fetus is large.
After six hours of active contractions, a second vaginal examination was performed: the cervix was dilated to six centimeters, the amniotic sac was absent. The head is pressed with a sagittal suture in a straight size, placing the small fontanel anteriorly.
Diagnosis: 38 weeks pregnancy, first stage of first full term birth. Transversely narrowed pelvis of the first degree, the fetus is large, straight high standing sagittal suture.
A decision was made to end the birth through surgery (large fetus, narrowing of the pelvis, incorrect insertion). C-section performed without complications, a child weighing 4.3 kilograms was removed.
Determining the size of the pelvis is extremely important, since their decrease or increase can lead to significant disruption of the course of labor. The most important during childbirth are the dimensions of the small pelvis, which are judged by measuring certain dimensions of the large pelvis using a special instrument - a pelvis gauge. The size of the large pelvis is determined using a Martin pelvis gauge (Fig. 6).
Rice. 6. Martin Tazomer.
The pelvis meter has the shape of a compass equipped with a scale on which centimeter and half-centimeter divisions are marked. At the ends of the branches of the tazomer there are spherical formations (“buttons”), which are applied to the protruding points of the large pelvis, somewhat squeezing the subcutaneous fatty tissue. To measure the transverse size of the pelvic outlet, a pelvis meter with intersecting branches was designed.
The examined woman lies on her back on a hard couch with her legs brought together and extended at the knee and hip joints. The doctor stands to the right of the pregnant woman, facing her. The branches of the pelvis are taken in such a way that fingers I and II hold the buttons. The graduated scale faces upward. Using your index fingers, you feel for the points, the distance between which is to be measured, pressing the buttons of the spread pelvis meter branches against them. The value of the corresponding size is marked on the scale.
The transverse dimensions of the pelvis (distantia spinarum, distantia cristarum, distantia trochanterica) and the external pelvic conjugata - conjugata externa are measured. (Fig. 7, 8).
Rice. 7. Measuring the transverse dimensions of the pelvis (1 - distantia spinarum, 2 - distantia cristarum, 3 - distantia trochanterica).
1. Distantia spinarum- the distance between the anterosuperior iliac spines on both sides; this size is 25-26 cm.
2. Distantia cristarum- the distance between the most distant parts of the iliac crests, this size is 28-29 cm.
3. Distantia trochanterica- the distance between the greater trochanters of the femurs; this distance is 31-32 cm (Fig. 9).
In a normally developed pelvis, the difference between the transverse dimensions of the large pelvis is 3 cm. A smaller difference between these dimensions will indicate a deviation from the normal structure of the pelvis.
4. Conjugata externa- the distance between the middle of the upper outer edge of the symphysis and the articulation of the V lumbar and I sacral vertebrae. (Fig. 8).
To measure it, a woman should lie on her left side, bending her left leg at the knee and hip joints, and keep her right leg extended. The “button” of one branch of the pelvis is installed in the middle of the upper outer edge of the symphysis, the other end is pressed against the suprasacral fossa, which is located under the spinous process of the V lumbar vertebra, corresponding to the upper corner of the sacral rhombus. You can determine this point by sliding your fingers downwards along the spinous processes of the lumbar vertebrae. The fossa is easily identified under the protrusion of the spinous process of the last lumbar vertebra. The external conjugate is normally 20-21 cm.
Rice. 8. Measurement of the external conjugate.
The external conjugate is important - by its size one can judge the size of the true conjugate (the direct size of the entrance to the pelvis).
To determine the true conjugate, subtract 9 cm from the length of the outer conjugate. For example, if the outer conjugate is 20 cm, then the true one is 11 cm.
The difference between the external and true conjugate depends on the thickness of the bones (sacrum, symphysis) and soft tissues. To determine the thickness of a woman’s bones, measure the circumference of the wrist joint (Soloviev index) with a centimeter tape (Fig. 9).
Rice. 9. Measurement of the Solovyov index.
Its average value is 14 - 16 cm. With the Solovyov index less than 14 cm (thin bones), the difference between the external and true conjugate will be less, so 8 cm is subtracted from the external conjugate. With the Solovyov index greater than 16 cm (thick bones), the difference between the outer and true conjugate will be larger, so 10 cm is subtracted from it.
Example: The external conjugate is 21 cm, the Solovyov index is 16.5 cm. What is the true conjugate? Answer: 21 cm - 10 cm = 11 cm (norm).
You can also calculate the size of the true conjugate by measuring the diagonal (Fig. 10).
Rice. 10 . Measuring diagonal conjugates.
Diagonal conjugate- this is the distance between the lower edge of the symphysis and the prominent point of the promontory. The easy accessibility of the cape indicates a decrease in the true conjugate. If middle finger reaches the promontory, then press the radial edge of the second finger to the lower surface of the symphysis, feeling the edge of the arcuate ligament of the pubis. After this, the point of contact is marked with the index finger of the left hand right hand with the lower edge of the symphysis. With a normally developed pelvis, the size of the diagonal conjugate is 13 cm. In these cases, the cape is unattainable.
If the cape is reached, the diagonal conjugate is 12.5 cm or less. By measuring the size of the diagonal conjugate, the doctor determines the size of the true conjugate. To do this, subtract 1.5-2.0 cm from the size of the diagonal conjugate (this figure is determined taking into account the height of the symphysis, the level of the promontory, and the angle of inclination of the pelvis). The higher the symphysis, the more difference between conjugates, and vice versa. When the height of the symphysis is 4 cm or more, 2 cm is subtracted from the value of the diagonal conjugate; when the height of the symphysis is 3.0-3.5 cm, 1.5 cm is subtracted. When the pelvic tilt angle is more than 50°, to determine the true conjugate, 2 is subtracted from the value of the diagonal conjugate cm. If the pelvic tilt angle is less than 45°, then subtract 1.5 cm.
There is another dimension of the large pelvis - lateral Kerner conjugate. This is the distance between the superior anterior and superior posterior iliac spines. Normally, this size is 14.5-15 cm. It is recommended to measure it with oblique and asymmetrical pelvises. In a woman with an asymmetrical pelvis, it is not the absolute size of the lateral conjugate that matters, but the comparison of their sizes on both sides.
If during examination of a woman there is a suspicion of a narrowing of the pelvis, then the dimensions of the exit plane are determined.
The dimensions of the pelvic outlet are determined as follows. The woman lies on her back, legs bent at the hip and knee joints, spread apart and pulled up to the stomach.
Straight exit plane size measured with a conventional pelvis meter (Fig. 11-a). One “button” of the pelvis gauge is pressed to the middle of the lower edge of the symphysis, the other to the top of the coccyx. In a normal pelvis, the size of the exit plane is 9.5 cm.
Rice. 11. Measuring the transverse (a) and direct (b) dimensions of the plane of entry into the pelvis.
Transverse dimension of the pelvic outlet plane(Fig. 11-b) - The distance between the inner surfaces of the ischial bones is quite difficult to measure. This size is measured with a centimeter or a pelvic gauge with intersecting branches in the position of the woman on her back with her legs brought to her stomach. 1.5 cm is added to the resulting size. Normally, the transverse size of the pelvis is 11 cm.
In the same position, women measure the pubic angle to assess the characteristics of the small pelvis by placing the first fingers of their hands on the pubic arches. With normal size and shape of the pelvis, the angle is greater than 90 degrees.
Indirect signs of a correct physique and a normal pelvis are the shape and size of the sacral rhombus (Michaelis rhombus)(Fig. 12).
Rice. 12. Michaelis rhombus (a - general form: 1 - depression between the spinous processes of the last lumbar and first sacral vertebrae; 2 - apex of the sacrum; 3 - posterosuperior iliac spines; 6 - shapes of the Michaelis diamond with a normal pelvis and various anomalies of the bony pelvis (diagram): 1 - normal pelvis; 2 - flat pelvis; 3 - uniformly narrowed pelvis; 4 - transversely narrowed pelvis; 5 - oblique pelvis).
The sacral rhombus is a platform on the posterior surface of the sacrum. In women with a normally developed pelvis, its shape approaches a square, all sides of which are equal, and the angles are approximately 90°. A decrease in the vertical or transverse axis of the rhombus, asymmetry of its halves (upper and lower, right and left) indicate anomalies of the bony pelvis. The upper corner of the diamond corresponds to the spinous process of the V lumbar vertebra. The lateral angles correspond to the posterosuperior iliac spines, the lower angle corresponds to the apex of the sacrum (sacrococcygeal joint).
The dimensions of the rhombus are measured with a measuring tape. Normally, the longitudinal size is 11 cm, the transverse size is 10 - 11 cm. The dimensions of the length of the Michaelis rhombus correspond to the dimensions of the true conjugate.
Questions for self-control
1. What instrument is used to measure the size of the female pelvis?
2. List the 4 main pelvic sizes.
3. How to measure distantia spinarum? What is this size?
4. What is distantia cristarum equal to?
5. How to measure the intertrochanteric size (distantia trochanterica)?
6. How to correctly measure the external conjugate? What position should a woman be in?
7. For what purpose and how is the Solovyov index measured?
8. What is a lateral conjugate? For what purpose is it necessary to measure it?
9. How to measure the direct and transverse dimensions of the pelvic outlet? What are they equal to?
10. What is a Michaelis rhombus? What shape does it have?
11. Name 3 ways to calculate the true conjugate.
12. How to measure a diagonal conjugate? What is it equal to?
