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. When examining, pay attention to the entire pelvic area, but special meaning attached to the sacral rhombus (Michaelis rhombus, Fig. 1), the shape of which, together with other data, makes it possible to judge the structure of the pelvis (Fig. 2).
Rice. 1. Sacral rhombus, or Michaelis rhombus
Rice. 2. Pelvic bones
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 tazomer 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. The following pelvic sizes are usually measured: (Latin names and abbreviations are indicated in parentheses, since the sizes are indicated that way in the exchange card.)
Spinarum distance (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
Treanteric 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 externa (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 in
hip and knee joints, the overlying one is pulled out. The external conjugate is normally 20-21 cm (Fig. 6).
Rice. 6. Measuring the outer conjugate
The external conjugate is important: by its size one can judge the size of the true conjugate - 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 it is often performed C-section. 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.
The 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, subtract 1.5-2 cm 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 pelvimetry. 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 by the results of an 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.
Many women, having learned about their new position, begin to worry about their physiology. In particular, we are talking about the size of the pelvis, since this largely determines how the pregnancy will proceed. Its narrowed shape almost always leads to various kinds of complications during childbirth. On your first visit antenatal clinic where every woman in the case successful conception is registered, attention is paid to this point. And in some cases, the expectant mother may be “delighted” with the diagnosis of a narrow pelvis during pregnancy.
But what is it, can there be any consequences, and how does childbirth generally proceed? All these questions worry many women. Well, let's try to figure it all out.
What should be understood by a narrow pelvis?
The pelvis of any woman is a formation of a dense, inextensible ring of bone structures. A child passes through it: first his head, then his body. At the same time, the cartilage tissue softens, which allows the ring to increase.
The female pelvis consists of 4 bones:
- 2 pelvic, which are formed by the iliac, pubic and
- Sacrum.
- Coccyx.
All of them are connected to each other through cartilage and ligaments. differs from the male one: it is wider, more voluminous, but at the same time has less depth. And if the normal parameters (we will touch on them a little later) of the pelvis in no way affect the course of labor, then if it deviates there can be serious complications.
In medical practice, there are two main types of narrow pelvis:
- Anatomical is a decrease in one or more parameters by 20 mm or a little more.
- Clinical - here we already have in mind the discrepancy between the child’s head and the woman’s bone ring.
At the same time, the functionality of the female pelvis may not always be impaired. For example, a child is small in size compared to a narrow pelvis. Equally and vice versa - if the pelvis has normal indicators, and the fruit is quite large. Here we can also talk about a clinically narrow pelvis.
Normal indicators
Let us now touch upon the normal parameters of the female pelvis. All measurements are carried out using a special tool - a pelvis meter. At the same time, they evaluate following sizes:
- Normally, the length between the anterior upper corners of the iliac bones is 25-26 cm.
- The distance between the farthest parts of the iliac crests should be from 28 to 29 cm.
- The distance between both femurs is 30-31 cm.
- The distance from the upper part of the symphysis to the suprasacral fossa is 20-21 cm.
The lumbosacral rhombus (Michaelis rhombus) has the following normal values: diagonally - 100 mm, and vertically - 110 mm.
Moreover, if the Michaelis rhombus has pronounced asymmetry or deviations in the size of the pelvis to a smaller side are observed, this indicates that the bones have an irregular structure.
Classification of the pelvic bones
As experts note, there are many types of narrowed pelvis. And often the obstetric literature reflects a classification based on morphological and radiological characteristics. According to them, the pelvis can be:
- Gynecoid. It is considered a normal type and occurs in 55% of all cases. With this body type, a woman with such a pelvis has a thin neck and waist, while the hips are wide. As for weight and height, everything is within normal limits.
- Android. This type is slightly less common - 20% and is typical for most men. Nevertheless, women with a masculine build can also have such a pelvis: wide shoulders, narrow hips, a thick neck and an undefined waist.
- Anthropoid. It is already 22%. In such a pelvis, the direct size of the entrance is increased, the transverse size is even larger. Such women are tall and lean. They have broad shoulders, and on the contrary, the waist and hips are narrow, the legs are thin and elongated.
- Platypeloid is the rarest type of pelvis, which occurs in only 3% of women. They are tall, thin, their muscles are underdeveloped, and their skin elasticity is noticeably reduced.
As for the shape of the small pelvis in women, it can also be very different. Of all the most common are:
- Generally uniformly narrowed or ORST. The most common form of the pelvis is 40-50% of all cases.
- Transverse contraction or Robert's pelvis.
- Flat. In turn, it is divided into several varieties: a simply flat pelvis, a flat-rachitic pelvis, a pelvis in which the wide part of the cavity is reduced.
At the same time, there are also those forms that are extremely rare:
- obliquely displaced;
- oblique;
- generally narrowed flat;
- funnel-shaped;
- kyphotic;
- spondylolisthetic;
- osteomalatic;
- assimilation.
Now it’s worth touching on the degree of narrowing of the pelvis in women, of which there are 4:
- 1st degree - conjugate sizes 9-11 cm.
- 2nd - conjugate sizes 7.5-8.9 cm.
- 3rd - conjugate sizes 6.5-7.4 cm.
- 4th - conjugate sizes less than 6 cm (absolutely narrow pelvis).
As many obstetricians note, I and II degrees of pelvic narrowing are mainly found.
Causes of a narrow pelvis
Most women, if they have a narrow pelvis, consider it individual feature its bone structure, acquired from its parents. In reality, this is not entirely true, although heredity also makes sense not to exclude. But as medical practice shows, in 90% of cases this problem, rather acquired than congenital.
The bone structure of an anatomically narrow pelvis is influenced by a variety of factors, and therefore it is quite difficult to take the necessary preventive measures. These include:
- Infectious diseases suffered in childhood.
- A poor diet in which the body receives insufficient amounts of essential micronutrients.
- Manifestations of frequent vitamin deficiency at a very young age.
- Imbalance hormonal levels in the body in adolescence.
- Diseases that affect the bone structure, previously suffered, such as rickets, polio, tuberculosis.
- Congenital skeletal deformity.
- There have been fractures or bruises of the pelvic bones in the past.
- Tumor in the pelvic area.
- The development of acceleration, when a girl grows only in height, while she remains narrow in width.
The reasons listed above relate to a transversely narrow pelvis during pregnancy or some other form of its anatomical nature. But there are still cases of its clinical form. More on this later.
Clinical form of the pelvis and its causes
The clinical form of a narrow pelvis can only be identified during childbirth, since it does not depend on its physical parameters. It is diagnosed only in cases where the child’s head exceeds the size of the bone ring. Typically, the clinical form can be diagnosed even in the absence of a narrow anatomical pelvis.
A diagnosis of this kind also has certain reasons:
- Long gestation period.
- Large fruit.
- Neoplasms in the uterus.
- The baby's head does not fit into the pelvis correctly.
- Hydrocele of the brain in the fetus.
- Any deviation in the development of the fetus in the womb.
Regardless of the type and parameters of the narrow pelvis during pregnancy, this is in any case a rather serious pathology. If this fact is ignored, the consequences can be severe.
Diagnosis
The likelihood of a narrow pelvis in a woman should be determined long before the birth of the child, which will avoid various kinds of complications. At the same time, during the diagnosis, it is important to pay attention to the medical history. That is, it is necessary to find out how women developed in childhood and puberty, whether there were any diseases or injuries.
To determine the narrow shape of the pelvis, an external examination is performed, measuring the size of the pelvis and fetus. In addition, other examinations are carried out:
- X-ray pelviometry.
The very first question that comes to the mind of a woman with a narrow pelvis during pregnancy: how to give birth in this case? During an ultrasound examination, it will be noticeable whether the size of the child’s head corresponds to the dimensions of the pelvic bones and exactly how it is located. If this is a facial or frontal presentation, then during childbirth the baby’s head needs more space.
X-ray pelviometry is performed only at the end of the third trimester. At this time, all tissues and organs of the fetus are fully formed. This procedure allows you to identify the shape of the woman’s bone structure, as well as determine the size of the fetal head and its compliance with standards.
It's only worth it to the expectant mother register with the antenatal clinic, the gynecologist will take all the necessary measurements of the pelvis. This is done using a special tool, which appearance resembles a compass and has a centimeter scale.
Visual observation
Suspicion of a narrow pelvis during pregnancy may arise even before visiting an antenatal clinic. There are visual signs that may indicate a narrow pelvis:
- The woman has brushes short length- 16 cm or slightly less.
- Small feet.
- In short ladies with a height of less than 165 cm, curvature of the spine, lameness and other gait disorders are clearly visible.
- The woman's previous births were complicated.
- Malfunctions menstrual cycle.
- Representatives with a masculine physique.
This is a kind of risk group that not every woman falls into.
From the moment when the expectant mother (if she has a narrow pelvis) registers with the antenatal clinic, she is under the close supervision of a gynecologist. Towards the end of the term, which is about a couple of weeks before the birth of the child, the mother is hospitalized in the antenatal department. Here the gestational age is clarified, the estimated weight of the fetus is determined, and other possible complications are identified.
In frequent cases, due to a woman’s narrow pelvis, the fetus takes incorrect position. Often we are talking about breech presentation, but there may be other cases: oblique and transverse.
In the last trimester, the expectant mother herself may notice some characteristic manifestations. For example, she experiences shortness of breath. This is due to the fact that the size of the narrow pelvis during pregnancy does not allow the baby’s head to press against the entrance to the small pelvic area. In those women who give birth for the first time, the abdomen takes on a pointed shape. Multiparous mothers have a sagging belly due to a weak abdominal wall.
What complications can there be?
Pregnancy against the background of a woman’s narrow pelvis can proceed practically without complications, or there may be a threat of interruption, regardless of the period. There may also be other complications in the form of gestosis, fetoplacental insufficiency. If the baby has a medium-sized head, then the birth can go smoothly. But often labor activity occurs with characteristic complications when a woman has a narrow pelvis.
Because of this bone anatomy, a woman’s water breaks prematurely. Due to untimely opening of the amniotic sac, the baby’s leg or arm falls out, which causes certain complications during childbirth - both the mother and the newborn increase the risk of birth trauma. Due to a prolapsed umbilical cord loop, the fetal head can be pinched, which leads to acute hypoxia and even fetal death.
In addition, a narrow pelvis can cause the fetal head to remain in the same plane for a long period of time. As a result, the pelvic organs experience fairly prolonged pressure. In turn, this can lead to subsequent tissue necrosis and the formation of vaginal fistulas. And if labor is very advanced, a rupture of the perineum, vulva, vagina, or uterus is possible.
Disturbances in the birth process often result in postpartum hemorrhage, as well as the development of lochiometra due to poor uterine contractility and lochial retention.
But what is much more dangerous, childbirth with a narrow pelvis in almost all cases poses a serious threat to the fetus:
- Often a child is born with asphyxia or in a hypoxic state.
- The fetus may have impaired cerebral circulation.
- Risk of traumatic spinal injury.
All these and some other complications may require observation by a neurologist, neurosurgeon, or resuscitation. therapeutic measures, including a long period of rehabilitation.
Labor activity
What exactly the birth will be like may depend on the anamnestic data, the anatomical shape of the narrow pelvis, its degree, the expected weight of the child and other complications. Childbirth may proceed naturally, but only if the child is small, is correctly presented, and also if the degree of pelvic narrowing is insignificant.
Due to early departure amniotic fluid The cervix dilates more slowly. In addition, an infection can enter the cavity of the reproductive organ, resulting in endometritis, placentitis, or the fetus itself is at risk. The first contractions are characterized by severe pain, and the first labor period lasts quite a long time.
As practice in the field of obstetrics shows, pregnancy and childbirth with a narrow pelvis are accompanied by rare and weak contractions in the first half. And the whole process can drag on for quite a long time, which leads to severe fatigue of the woman in labor.
During the second labor period there may be certain difficulties associated with the advancement of the baby's head. Wherein painful sensations become more intense, and the woman experiences general fatigue.
The need for a caesarean section
Indications for surgical intervention can be absolute and relative. The first of them include following cases:
- Narrow pelvic shape III or IV degree.
- The deformation of the woman's pelvis is pronounced.
- The joints and the pelvic bones themselves have damage caused by previous labor.
- The presence of a tumor in the pelvic bones.
Based on the listed signs, the child can only be born by caesarean section. This procedure is carried out as planned, starting from the moment of birth or from the appearance of the first contractions.
Relative indications include the following:
- Anatomically narrow pelvis of the II degree.
- I degree of narrow pelvis against the background of other additional factors.
- Large child.
- Breech presentation fetus
- Post-term pregnancy.
- Fetal hypoxia.
- A scar on the uterus from a previous birth operation.
- Abnormalities of the genital organs.
If these relative factors are present, a woman can still try to give birth naturally. However, if during labor activity The condition of the expectant mother will begin to deteriorate, and if a serious threat to her and the child is identified, a caesarean section is performed.
Every pregnant woman, especially those with a narrow pelvis, should listen to the advice of a specialist. Only he will be able to give recommendations on exactly how childbirth can take place in each specific case. But only if there is a danger to the child or he is at risk of injury, you will have to resort to surgical delivery. And this will be the truest and only the right choice.
For any woman, bearing a child is the most pleasant moment in her life. Mom immediately begins to take care of herself and lead a more correct lifestyle. This also applies to those women who have been diagnosed with a narrow pelvis. However, there is no cause for concern here, and the baby can be born completely healthy and healthy. To do this, the main thing is to follow all the doctor’s recommendations. Then the entire pregnancy will go smoothly, and childbirth will take place without serious complications.
As a conclusion
It is worth noting that a narrow pelvis is a fairly common diagnosis. But! Despite this, many women with a similar bone structure could give birth to healthy children without complications. In this regard, you should not be afraid of such a “terrible” diagnosis - a narrow pelvis. If the degree of narrow pelvis during pregnancy is not too severe, then childbirth can occur naturally.
Otherwise, a caesarean section will be performed, which will allow the child to be born unhindered, and the woman will be able to hug him, becoming a full-fledged mother.
During pregnancy, gynecologists pay increased attention to the size of the expectant mother's pelvis. In our article we will look at what standards should be for natural birth, and also what to do if you have a deviation from the norm.
Measuring the size of the pelvis during pregnancy
A mandatory procedure is to determine the size of this area. This is necessary to determine whether natural resolution is possible or whether surgical intervention will have to be resorted to.
Important! To determine the internal narrowing, obstetricians measure the girth of the wrist using the Solovyov index: if the girth exceeds 14 cm, then the presence of a narrow pelvis can be assumed.
The structure and measurements are determined by doctors by palpation and using a pelvis meter. The measurement is carried out several times: first when a woman registers, and then before the birth itself. Special attention is devoted to the study of the sacral region - the Michaelis rhombus. To do this, measurements are taken between the dimples above the tailbone. If the diamond is a square whose diagonals are approximately 11 cm, then we can conclude that there is no deformation. If they are different, then we can assume that the pregnant woman has a pathology. 
Measurements are carried out as follows:
- The woman should lie on her back, provide access to her thighs, and remove clothing from this area.
- Using a pelvis meter, the doctor takes 1 longitudinal and 3 transverse measurements.
- Distantia spinarum- line between the anterior superior iliac spines - approximately 26 cm;
- Distantia cristarum- the greatest distance between the iliac crests is 24-27 cm;
- Distantia trochanterica- line between the greater trochanters of the femur bones - 28-29 cm;
- Conjugata externa- the line between the upper edge of the pubic symphysis and the V-lumbar vertebra - 20-21 cm.
Normal pelvic parameters
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Narrow pelvis
Let's consider when it is considered narrowed, and what to do in case of such a pathology for a pregnant woman.
Did you know? Only in 5% of cases are children born within the period prescribed by doctors. In other cases, birth occurs 7-10 days earlier than the expected date.
First, it is worth noting that it is customary to distinguish two concepts - anatomically and clinically narrow pelvis. An anatomically narrow pelvis is characterized by a decrease in measurements by at least 1.5-2 cm. In some situations, childbirth proceeds well - this happens if the child has a small head. 
A clinically narrow pelvis may well correspond to normal measurements, but due to the fact that the child may have a large head, a discrepancy arises between the head and pelvis. In such a situation, childbirth can cause difficulties in the health of mother and baby, so doctors often consider the possibility of performing an operation.
Causes
- The main causes of an anatomically narrow pelvis include:
- presence of rickets;
- poor nutrition in childhood;
- presence of polio;
- the presence of congenital anomalies;
- presence of pelvic fractures;
- presence of tumors;
- the presence of kyphosis, scoliosis, spondylolisthesis and other deformities of the spine and coccyx;
- the presence of diseases and dislocations of the hip joints; rapid growth during puberty elevated level
- androgens;
the presence of strong psycho-emotional and physical stress in adolescence.
Effect on the course of pregnancy 
The presence of pathology has almost no effect on the course of pregnancy. If you have an anatomically narrowed pelvis, you should definitely see a doctor. In the last trimester, some difficulties often arise, for example, the baby’s incorrect position. Since the head is not able to press against the entrance to the pelvis due to the fact that it is narrow, the woman may suffer from shortness of breath.
Pregnancy management Women with pathology are placed on special registration. This is due to the fact that there is a high risk of complications during pregnancy. Also, the due date is determined with particular accuracy - this will eliminate post-maturity, which negatively affects the general condition of the woman and baby. Approximately 1-2 weeks before giving birth, it is recommended to hospitalize a pregnant woman to clarify the diagnosis and choose a method of delivery.
Indications for caesarean section
There are two types of indications for intervention. Let's look at them. Absolute readings:
- the presence of a narrow pelvis of 3 and 4 degrees;
- presence of severe pelvic deformity;
- damage to the joints of the pelvic bones;
- presence of bone tumors.
Important! During contractions, women with this pathology are advised to lie down more so as not to damage the amniotic sac, as it can provoke too early rupture of amniotic fluid.
Relative indications are the presence of a narrowed pelvis of the 1st degree simultaneously with the following factors:
- large fruit;
- presentation in the pelvic area;
- excess of pregnancy;
- child suffocation;
- uterine scar;
- abnormal deviations of the genital organs.
Possible complications during childbirth
Unfortunately, if you have an anatomically narrow pelvis, it is impossible to give birth on your own. This is explained by the fact that it is very difficult for a child to overcome the path, and this can lead to injuries and even death. It is for these reasons that obstetricians strongly advise women with this pathology to perform a planned caesarean section. However, if there is 1 degree of narrowing, the expectant mother may be allowed to give birth on her own.
But such a decision may lead to:- early rupture of amniotic fluid;
- weakened activity during childbirth;
- placental abruption;
- rupture of the pelvic ligaments;
- uterine rupture;
- hemorrhages;
- fetal suffocation;
- injury to the baby.
Did you know? A newborn baby has 300 bones, while an adult has only 206.
A narrow pelvis is a specific structural feature of the female body. But even with such a pathology, modern medicine makes it possible to carry a pregnancy to term and give birth to a child. The main thing is to follow the doctor's instructions and take care of yourself. Video: female pelvis during pregnancy
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Dimensions of the pelvic inlet.
Bone ring of the entrance of the normal pelvis adult woman has the shape of a transverse oval. In this oval, dimensions are distinguished, going in three directions.
The direct size of the entrance (Fig. 87) - the distance from the middle of the upper edge of the symphysis (on its posterior surface) to the prominent point of the promontory of the sacrum - is 11 cm; this size is called true conjugata 1.
In obstetrics, two true conjugates are distinguished (Fig. 96). The conjugate just mentioned is an anatomical true conjugate; the other conjugate passes to the same point of the promontory of the sacrum, but not from the upper edge of the symphysis, but slightly lower, from the tubercle on the inner surface of the symphysis - this is the obstetric true conjugate; it is slightly (0.2 - 0.3 cm) shorter than the anatomical one.
The transverse size of the entrance - the distance between the most distant points of the nameless lines - is 13 cm (Fig. 87).
The oblique dimensions of the entrance go from the upper edge of the sacroiliac joint on the right and left to the iliopubic tubercle of the opposite side; oblique entrance size is 12 cm.
The shortest size of an ellipse is called a conjugate.
There are right and left oblique sizes (Fig. 87); the right one goes from the right sacroiliac joint to the left iliopubic tubercle; left oblique dimension - from the left sacroiliac joint to the right iliopubic tubercle. Thus, the directions of oblique dimensions are determined by the back point from which they begin.
It is extremely important to be well versed in this, since these directions are used to determine the position of the presenting part of the fetus in the pelvis.
In the pelvic cavity, the sizes of the wide and narrow parts are distinguished separately.
The dimensions of the upper, or wide, part of the pelvic cavity.
The straight dimension goes from the middle of the posterior surface of the symphysis to the connection of the II sacral vertebra with the III sacral vertebra; it is 12.5 cm.
The transverse dimension passes between the inner surfaces of the bottom of the acetabulum; it is 12.5 cm.
The oblique dimensions of the wide part of the pelvic cavity are the distance from the upper edge of the greater sciatic notch (incisura ischiadica major) on one side to the upper edge of the obturator foramen (foramen obturatorium) on the other side. Each of these sizes is 13 cm.
The dimensions of the lower, or narrow, part of the pelvic cavity. Straight size - from the lower edge of the symphysis to the apex of the sacrum; it is equal to 11.5 cm.
Transverse size - the distance between the ischial networks; it is equal to 10.5 cm.
This part of the pelvic cavity has the shape of an oval, slightly elongated in the anteroposterior direction, approaching the standing oval.
Dimensions of the pelvic outlet. The direct size (Fig. 88) - the distance from the lower edge of the symphysis to the apex of the coccyx - is 9 -9.5 cm. During labor, the pressure of the incoming presenting part of the fetus causes the apex of the coccyx to bend backward by 1 - 1.5 cm, which is why the direct size of the outlet may increase up to 11 cm.
The transverse size of the outlet (Fig. 88) - the distance between the inner sides of the ischial tuberosities - is 10.5 cm; the outlet of the pelvis has the shape of a standing oval.
Sections of the pelvis |
Dimensions in cm |
Shape (schematically) |
||
transverse/oblique |
||||
Entrance.................................. |
Transverse oval |
|||
plane of the wide part. |
Oval lying obliquely Oval approaching a straight position |
|||
narrow part plane |
||||
Exit............................. . |
Upright oval |
|||
Thus, at the entrance of the pelvis largest size is transverse; in the cavity - oblique, in the outlet - straight size. If we look into the pelvic canal from above, comparing the size and shape of all parts of the small pelvis, we will see that the lumen along its entire length is schematically represented as follows: at the entrance it has the appearance of a transversely lying oval; descending lower, the oval gradually takes on a slightly oblique position; descending even lower, it gradually turns and in the lowest part of the lumen of the pelvic canal, at the outlet of the pelvis, takes the position of a standing oval.
Rice. 88. Pelvic outlet and its dimensions (straight and transverse).
This shape of the individual parts of the pelvic cavity to some extent explains the different position of the presenting part of the fetus in different parts of the pelvic canal. We will return to this when studying the mechanism of childbirth.
Determination of a true conjugate by the outer conjugate. To calculate the true conjugate from the external conjugate, 9 cm is subtracted from the length of the external conjugate. Thus, with an external conjugate equal to 20 cm, the true conjugate is determined to be 11 cm. It is clear that this calculation is approximate, since there are a number of points that make it difficult to accurately calculate, such as, for example, different thicknesses of soft tissues and bones themselves.
Determination of a true conjugate from a diagonal conjugate. More precisely, you can determine the length of the true conjugate by the diagonal conjugate (conjugata diagonalis). To determine the diagonal conjugate, i.e. the distance from the lower edge of the symphysis to the prominent point of the promontory of the sacrum, it is necessary to make vaginal examination, observing the rules of asepsis and antiseptics (see Chapter VIII).
Using the ends of the fingers, they first palpate the anterior wall of the pelvis, identify the structure of the posterior surface of the symphysis, determine whether there are bony protrusions (exostoses) that reduce the size of the pelvis, determine the approximate height of the symphysis, then palpate side walls pelvis and also determine whether there are any deformations here. 
Rice. 89. Measurement of diagonal conjugates (first moment).
Rice. 90. Measuring diagonal conjugates (second point).
Along the way, they find out the condition of the vagina (narrow, short) - all this is important for taking into account the nature of the upcoming birth. Finally, along the posterior wall of the vagina, along the sacral cavity, they move upward and try to reach the promontory of the sacrum. In a normal pelvis, it is possible to reach the promontory only if the examining midwife has long fingers. Usually when medium length fingers of the examining hand, if the promontory is not reached, the diagonal conjugate is considered normal, i.e. equal to 12.5 cm.
The diagonal conjugate can to a certain extent be considered as the hypotenuse of a right triangle, in which one side is the symphysis, the other is the true conjugate (Fig. 96). Having the ability to measure the diagonal conjugate and the height of the symphysis (Fig. 94), i.e., knowing the length of the hypotenuse and one of the legs, we can calculate the length of the other leg.
Rice. 91. Measurement straight size pelvic outlet.
If the promontory is reached, then, resting against it with the end of the middle finger of the examining hand, with the end of the index finger of the other hand (Fig. 89) mark on the examining hand the place where it touches the lower edge of the symphysis; The marking index finger is not taken away, but the fingers are removed from the vagina along with the mark. Then they ask the nanny or, in extreme cases, the pregnant woman to measure the distance from the mark to the end of the middle finger with a centimeter tape, or better yet, with a hip gauge (Fig. 90) - this will be the length of the diagonal conjugate. To determine the size of the true conjugate, an average of 1.5 to 2 cm is subtracted from the length of the diagonal conjugate, accounting for the difference in length between the two conjugates.
Determination of the size of the pelvic outlet. To determine the size of this section of the pelvis, the woman is placed in a supine position with her thighs pressed to her stomach.
The direct size of the pelvic outlet is measured from the lower edge of the symphysis to the apex of the coccyx (Fig. 91).
The transverse size of the outlet is the distance between the ischial tuberosities. First, the ischial tuberosities are felt with your fingers and the buttons of a special pelvis are tightly pressed to the inner surfaces of these tuberosities, or this distance is measured with a centimeter tape (Fig. 92). To the size obtained in this way, add 1 - 1.5 cm, depending on the thickness of the subcutaneous fat layer. 
Rice. 92. Measuring the transverse size of the pelvic outlet.
The size of the pelvic outlet can also be judged by the size of the pubic angle. In a normal female pelvis this angle is obtuse; The smaller the pubic angle, the closer the ischial tuberosities are located to each other. Approximately it can be measured as shown in Fig. 93.
Oblique pelvic dimensions
Pelvic asymmetry is determined based on measuring the oblique dimensions of the pelvis. To do this, compare the distances between the following points:
- from the middle of the symphysis to the posterosuperior iliac spines on the right and left (for a normal pelvis 17 cm);
Rice. 93. Measuring the size of the pubic angle
- from the anterior superior spine of one side to the posterior superior spine of the opposite side and vice versa (for a normal pelvis 21 cm);
3) from the spinous process of the V lumbar vertebra to the anterior superior spine of the right and left ilium (for a normal pelvis 18 cm). 
Rice. 94. Determination of the height of the symphysis
In a symmetrical pelvis, these paired dimensions are the same; if one is larger and the other smaller, then the pelvis is asymmetrical, oblique. The difference in the size of the oblique dimensions determines the degree of this distortion. The asymmetry of the pelvis can be judged to some extent by the shape of the lumbar diamond (p. 357).
Measuring the height of the symphysis
If, for example, when measuring the diagonal conjugate, the latter turns out to be shorter than usual - let’s say that it is not 12.5, but 12 cm, then in order to more accurately determine the length of the true conjugate, it is important to know the height of the symphysis in this woman. If it turns out that the symphysis
below 4 cm, approximately 3.5 cm, then the true conjugate may be normal even with a diagonal conjugate equal to 12 cm. Thus, depending on the height of the symphysis, the difference in length between the true and diagonal conjugate varies. To measure the height of the symphysis, a bent index finger is passed along the posterior surface of the symphysis and pressed firmly against it with the palmar surface (Fig. 94). Having reached the upper edge of the symphysis with the end of the examining finger, use the index finger of the other hand to mark the point of contact with the lower edge of the symphysis and then measure the distance between the end of the examining finger and the mark on it - this will be the height of the symphysis; On average, a height of 4 cm is considered normal.
For example, if the height of the symphysis is more than 4 cm, to determine the true conjugate, you should subtract not 1.5, but 2 cm from the length of the diagonal conjugate.
No matter how far medical science steps forward, it will definitely take with it into the future an ancient and very simple instrument - pelvisometer. With its help, any obstetrician can predict how childbirth will proceed for a woman who has just registered for pregnancy. How is the size of the pelvis measured? What are they and what do they affect?
Why do pregnant women have their pelvic size determined?
Observing the mystery of childbirth, our distant ancestors naively believed that during pushing, the mother’s womb opens to push out the fetus, and then contracts again. It is truly difficult to imagine how otherwise a full-term baby with a head circumference of at least 30 cm could be born!
But in fact, a woman’s birth canal has a powerful and almost inextensible bone frame, and the birth process is subject to complex laws of biomechanics. According to them, the child must enter the birth canal in a certain position, gradually turn, and in a strictly defined position cut through the tissue of the perineum, leaving the mother’s womb. But even if all these rules are followed, there are situations when, due to a discrepancy between the sizes of the pelvis and the fetus, labor is painfully delayed or cannot end on its own. Until the middle of the last century, the main cause of birth injuries and death of a baby or woman in labor was an anatomically or clinically narrow pelvis. Just remember the wife of Andrei Bolkonsky...
The main purpose of measuring the size of a pregnant woman’s pelvis is to determine what size child she can give birth to on her own, so that neither the baby nor the mother are harmed. The doctor predicts in advance how serious problems during childbirth may be and chooses the most optimal type of care for the woman. For example, in a situation where a narrow pelvis is diagnosed, a woman in labor is offered a planned caesarean section.
How to determine the size of the pelvis
Obstetricians are not interested in the size of everything, but only. This is the bony birth canal through which the fetus moves outward during contractions and pushing. Measuring it from the inside is technically very difficult or not safe during pregnancy (such as using x-rays). And on the outside it is covered not only with an array of pelvic and femur bones, but also with powerful muscles and subcutaneous fat. Therefore, the doctor determines the external dimensions with a pelvis and from them, using special time-tested formulas, imagines what the internal volume of the pelvic ring will actually be. To measure only some indicators, a vaginal examination and a centimeter tape are sufficient.
What determines the size of the pelvis in obstetrics?
First, the obstetrician-gynecologist will ask the pregnant woman to turn her back to him and probe sacral area (Michaelis rhombus). It's good when it's shaped like a square. The narrower it is, the more likely that a woman has a narrow pelvis.
Next, the patient lies on the couch on her back, straightening her legs. The doctor applies the button-shaped tips of the pelvis gauge to the most prominent anterior-outer points of the wings of the pelvic bones. In the figure this is - normally it is 25-26 cm. Then the doctor stretches the compasses-like legs of the pelvis a little more and presses its buttons from the sides: to the most distant points of the wings of the ilium. This in the figure is normally larger than the first by at least 3 cm. By spreading the legs of the pelvis further apart, the obstetrician lowers it lower - to the trochanters of the femurs. This one is another 3 cm larger. To measure the latter, a woman needs to turn on her side, bending the lower leg at the joints. The doctor places one button of the pelvis gauge to the center of the pubic joint, and the other on the back in the hole above the first sacral vertebra. This is how the outer conjugate is determined, normally equal to at least 20 cm.
But if obstetricians were guided only by the external dimensions of the woman in labor, they would make many fatal mistakes. After all, the thickness of bones varies greatly from person to person. Therefore, the next step of the gynecologist will be measuring a woman's wrist circumference. This is how the thickness of the bones is determined, taking into account which the size of the internal conjugate is empirically calculated. This is the very exit from the pelvis that the fetus will have to overcome during childbirth. There is a direct relationship: the smaller the circumference at the narrowest point of the wrist, the thinner the bones and the less must be subtracted from the size of the external conjugate. Approximately, we can say that with a wrist size of 14 cm or less, the pelvis will be normal.
Next, the doctor will determine internal dimensions of the pelvis during gynecological examination . Every doctor knows the length of his palm from the crease at the base between the first and second fingers to the tip of the middle one. Having inserted his fingers into the pregnant woman’s vagina, with the third he will try to reach the promontory of the sacrum, noticing at the same time how tightly the base of his first finger adheres to the pubic joint (this is in the diagram). If this turns out to be at least 12.5 cm, or even better - it is not possible to reach the sacrum at all - the pelvis will freely “pass” the child’s head.
In order to more fully judge the size of the exit from the pelvic ring, the pelvis gauge also measures the distance between the lower edge of the center of the pubis and the top of the coccyx (normally, with a deduction of 1.5 cm for soft tissue, from 9.5 cm or more), as well as between ischial tuberosities (here it’s the other way around - add 1.5 cm and get a normal value of 11 cm and above).
Not so simple…
Every woman is unique, and so is the shape and size of her pelvis. It can be not only wide or narrow, but also oblique, and in any plane. Its structure is influenced by scoliosis, osteochondrosis, and congenital degenerative diseases, which a woman may not even be aware of. Inside the pelvic ring, the bone may have outgrowths (osteophytes), making the largest circle dangerously traumatic or even impassable for the fetus. Therefore, the doctor can take a few more external measurements and send for an ultrasound to clarify the internal ones and identify osteophytes. Therefore, if the doctor considers it necessary to carry them out, be glad that you are being examined by an attentive gynecologist. Believe me: it’s worth being patient for the sake of a successful outcome of the birth.
