Pelvic capacity is usually assessed based on the analysis of digital indicators obtained from instrumental measurements. To measure the pelvis, a special instrument is used - a pelvis meter (Fig. 12).
Rice. 12. Types of basin meters.
a - with non-crossing branches (regular model); b - with intersecting branches. 
Rice. 13. Measuring the transverse dimensions of the pelvis.
Rice. 14. Measurement of external conjugate.
A compass is used to measure the distance between certain points of the body - the protrusions of the bones. When measuring the pelvis instrumentally, it is necessary to take into account the development of the subcutaneous fat layer. The pelvis is measured with the woman lying down, but it can also be done in a standing position.
Three transverse dimensions are measured with a compass:
1) the distance between the anterosuperior spines (distantia spinarum), equal to 25-26 cm;
2) the distance between the crests of the iliac bones (distantia cristarum), equal to 28-29 cm;
3) distance between trochanters femur(distantia trochanterica), equal to 30-31 cm.
When measuring the distance between the spines, the ends of the compass are placed on the outermost points of the anterosuperior spines, at the site of attachment of the tendon m. sartorius; when measuring the distance between the combs - to the most distant points along the outer edge of the ossis ilei and when measuring the distance between the trochanters - to the points most distant from each other on the outer surface of the trochanters (Fig. 13).
When measuring external straight size pelvis (conjugata externa) the woman is in a position on her side; in this case, one leg (lower) should be bent at the hip and knee joints, and the other leg (upper) extended. One leg of the compass is placed on the anterior surface of the symphysis near its upper edge, and the other in the depression (on the ligament) between the last lumbar and first sacral vertebrae ( top corner) (Fig. 14). The external direct size, or external conjugate, is 20-21 cm. Measuring the external conjugate allows us to indirectly judge the size of the true conjugate (conjugate vera). To determine the size of the true conjugata, it is recommended to subtract 9.5-10 cm from the external direct size. However, this definition of conjugata vera is inaccurate and is only indicative. The internal straight size (conjugata vera) is 11 cm.
Another external size, the so-called lateral conjugate (the distance between the anterosuperior and posterosuperior iliac spines of the same side), allows us to get a certain idea of the internal dimensions of the pelvis. At normal sizes its size varies between 14.5 and 15 cm; with flat pelvises it is 13.5-13 cm or less. In cases where the size of the lateral conjugate on one side is larger or smaller than on the other, it can be assumed that there is asymmetry of the pelvis - an oblique narrowing of the latter.
For approximate determination transverse size of the entrance to the small pelvis, you can divide the distance between the scallops (29 cm) in half or subtract 14-15 cm from it.
In cases where there are deviations from the normal dimensions of the pelvis, not to mention the presence of obvious deformations on the part of the bone skeleton, it is necessary to carry out thorough examination and measuring the pelvis using a vaginal examination, which will be discussed later. IN necessary cases The pelvic outlet is also measured. In this case, the subject is in a horizontal position, her legs are bent at the hips and knee joints, pulled up to the stomach and laid aside.
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)
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Pelvic plane |
Landmarks |
Dimensions (cm) |
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Straight (cm) |
Transverse (cm) |
Oblique (cm) |
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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) |
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Wide part |
Middle inner surface pubic arch, middle of smooth plates, 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 |
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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 |
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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 |
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True conjugate.
True, or obstetric, conjugate(conjugata vera, s. obstetrica) is the shortest distance between the promontory and the most prominent point in 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 incisura jugularis to spinous process 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 when vaginal examination women, which is produced in compliance with all 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.
1. Transverse diameter, diameter transversa- the distance between the most distant points of both boundary lines.
2. Oblique diameter, diameter obliqua(dextra et sinistra) - measured from the right (left) sacroiliac joint to the left (right) iliopubic eminence.
3. Diagonal conjugate, conjugata diagonalis- the distance from the lower edge of the symphysis to the most prominent point of the sacral promontory. (normally 12.5-13 cm)
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. It is not always possible to measure the diagonal conjugate, because with normal pelvic sizes the promontory is not reached or is difficult to palpate. If the promontory cannot be reached with the end of an extended finger, the volume of this pelvis can be considered normal or close to normal.
3.1. True conjugata, diameter conjugata- the distance from the posterior surface of the pubic symphysis to the most prominent point of the sacral promontory.
To determine the true conjugate, subtract 1.5-2 cm from the size of the diagonal conjugate.
3.2. Anatomical conjugate- the distance from the upper surface of the pubic symphysis to the most prominent point of the sacral promontory.
4. Distantia spinarum- the distance between the superior anterior iliac spines. (normally 25-26 cm)
5. Distantia trochanterica- distance between large skewers femurs. (normally 30-31 cm)
6. Distantia cristarum- the distance between the most distant points of the iliac crest. (normally 28-29 cm)
When determining the size of the pelvis, it is necessary to take into account the thickness of its bones; it is judged by the value of the so-called Solovyov index - circumference wrist joint. The average index value is 14 cm. If the Solovyov index is more than 14 cm, it can be assumed that the pelvic bones are massive and the size of the small pelvis is smaller than expected.
Michaelis rhombus In a standing position, the so-called lumbosacral rhombus, or Michaelis rhombus, is examined. Normally, the vertical size of the rhombus is on average 11 cm, the transverse size is 10 cm. If the structure of the small pelvis is disturbed, the lumbosacral rhombus is not clearly expressed, its shape and size are changed.
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 natural birth canal. The results of the pelvic examination are entered into medical documents. 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. Pelvic bones
The most important of all methods of examining the pelvis is 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: (Indicated in parentheses Latin names and abbreviations, since the dimensions 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
External conjugate (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). Diagonal conjugate at normal pelvis equals 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 next step. 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 necessary, 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. X-ray examination pelvis - 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 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.
During pregnancy increased attention Gynecologists pay 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
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 internal narrowing, obstetricians measure the girth of the wrist using the Solovyov index: if the girth exceeds 14 cm, then we can assume the presence narrow pelvis.
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 pelvic 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 big head, there is a discrepancy 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 activity 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. Difficulties in management lie in the fact that it is very important to identify the abnormal position of the fetus in time. Also, the due date is determined with particular accuracy - this will eliminate post-maturity, which negatively affects general state women 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, to the expectant mother may be allowed to give birth on their 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.
Narrow pelvis - specific feature structure of the female body. But even with such a pathology modern medicine allows you to endure pregnancy 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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