Normal size of the female pelvis. Determining the size of the pelvis

The plan of examination of a pregnant woman necessarily includes a measurement of the pelvis. This procedure is often carried out at the first appointment for every woman who has turned to an obstetrician-gynecologist about a desired pregnancy. Bone pelvis and soft tissues lining it are the birth canal through which the baby is born. It is extremely important for doctors and a woman to know if the birth canal is small for a baby. This circumstance determines the possibility of childbirth through natural birth canal. The results of the pelvic exam 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 the pelvis of a pregnant woman.

Pelvic measurement 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 childbirth or present insurmountable obstacles for them.

The study of the pelvis is carried out by inspection, palpation and measurement. On examination, attention is paid to the entire pelvic region, but special importance is attached to the sacral rhombus (Michaelis rhombus, Fig. 1), the shape of which, in combination with other data, allows one to judge the structure of the pelvis (Fig. 2).

Rice. 1. sacral rhombus,or the Michaelis rhombus

Rice . 2. Bonespelvis

Most importance of all methods of pelvic examination has its measurement. Knowing the size of the pelvis, one can judge the course of childbirth, about possible complications with them, on 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, therefore, the external dimensions of the pelvis are usually measured and they are used to approximately judge the size and shape of the small pelvis. The pelvis is measured with a special instrument - a pelvis meter. The tazomer has the form of a compass, equipped with a scale on which centimeter and half-centimeter divisions are applied. At the ends of the branches of the tazomer there are buttons; they are applied to the places, the distance between which is to be measured.

The following pelvic sizes are usually measured: (In parentheses are indicated Latin names and abbreviations, since the sizes are indicated in the exchange card in this way.)

Distant spinarum (Distantiasplnarum D.sp.)- the distance between the anterior-superior iliac spines. This size is usually 25-26 cm (Fig. 3).

Rice. 3. Measuring the spinarum distance

Distantia cristarum (Distantiacristarum D. Cr.)- the distance between the most distant points of the iliac crests. It averages 28-29 cm (Fig. 4).

Rice. 4. Measuring the distance of the cristarum

Trianteric distance (DistantiatrochantericaD. Tr.)- distance between large skewers thigh bones. This size is 31 -32 cm (Fig. 5).

Rice. 5. Measuring the distance of the triangular

Krnjugata externa (Conjugata externa C. Ext.)- external conjugate, i.e. straight size of the pelvis. 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 pulled out. The outer conjugate is normally 20–21 cm (Fig. 6).

Rice. 6. Measurement of external conjugates

External conjugate is important: by its value one can judge the size true conjugate- the distance between the sacral cape - 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). it smallest size inside the pelvis through which the fetal head passes during childbirth. If the true conjugate is less than 10.5 cm, then childbirth through the natural birth canal may be difficult or simply impossible; in this case, a caesarean section is often performed. To determine the true conjugate, 9 cm is subtracted 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 is 18 cm long, then the true conjugate is 9 cm, and so on. The difference between the outer and true conjugates depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of the bones and soft tissues in women is different, so the difference between the size of the outer 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) called 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 (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 when normal sizes pelvis during vaginal examination, the cape of the sacrum is not reached by the researcher's finger or is palpated with difficulty. If, during a vaginal examination, the doctor does not reach the cape, 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 the examination of a woman there is a suspicion of a narrowing of the pelvic outlet, then the dimensions of this cavity are determined. These measurements are not mandatory, and they are measured in a position in which the woman lies on her back, her legs are bent at the hips and knee joints, divorced to the side and pulled up to the stomach.

The definition of the shape of the pubic angle is important. With normal pelvic dimensions, it is 90-100 °. The shape of the pubic angle is determined next trick. The woman lies on her back, her legs are bent and pulled up to her stomach. Palmar side thumbs applied close to the lower edge of the symphysis. The location of the fingers allows you to judge the magnitude of the angle of the pubic arch.

Additional Research

If necessary, to obtain additional data on the size of the pelvis, its compliance with the size of the fetal head, deformities of the bones and their joints, an x-ray examination of the pelvis is performed - X-ray pelviometry. Such a study 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 in the position of a woman lying on her back and on her side, which allows you to establish the shape of the sacrum, pubic and other bones; a special ruler determines the transverse and direct dimensions of the pelvis. The head of the fetus is also measured, and on this basis it is judged that 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 research. 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 unbent, that is, the forehead or face is present, then it needs more space than in cases where the occiput is present. Fortunately, in most cases, childbirth takes place in the occipital presentation.

With external pelvic measurement, it is difficult to take into account the thickness of the pelvic bones. Of known importance is the measurement of the circumference with a centimeter tape wrist joint pregnant (Soloviev index). The average value of this circumference is 14 cm. If the index is larger, it can be assumed that the pelvic bones are massive and the dimensions of its cavity are smaller than would be expected from the measurements of the 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.

A long time ago, the time when a narrow pelvis was a kind of sentence for a woman in labor is gone. modern medicine allows you to ensure a successful outcome of childbirth, regardless of the structural features of the pelvis of a woman. But for this, doctors must take the necessary measurements in a timely manner. And every woman should be aware of the significance of this procedure.

The dimensions of the pelvis during pregnancy are measured already at 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

Normal natural delivery depends on the structure and size. Violation of symmetry, deviations and anomalies often lead to complications during pregnancy and during childbirth. Measurements become especially important if the ultrasound reveals the presentation of the baby, then maximum care from the doctors will be required.

Normal pelvic dimensions in obstetrics during pregnancy

First of all, doctors need to measure the Michaelis diamond or lumbosacral diamond, which is assessed while standing at the back of the sacrum and should have a symmetrical shape. AT normal condition the vertical length is 11 cm, and the width is 10 cm. Any deviations, non-standard shape and a fuzzy diamond-shaped silhouette indicate difficulties as the 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;
• length between large skewers of 2 femurs - 30-32 centimeters.

Table of normal values ​​​​of the size of the pelvis during pregnancy:

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 value of a wide and narrow pelvis during pregnancy

A narrow pelvis is stated 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 is reduced to 2 cm. Diagnosing a narrowing does not necessarily indicate pathological difficult childbirth. Often in women with narrow parameters, a small baby is born, and the head passes without difficulty. The indicator is measured for the purpose of assessing the risks if a pregnancy develops inside the womb. large fruit, this often leads to grave consequences during natural spontaneous childbirth.

Narrow pelvis - risk factors for pregnant women

According to statistics, pregnant women with narrow hips are much more likely to be diagnosed with fetal presentation. Therefore, they belong to the group requiring careful monitoring from the outside. medical specialists to reduce the likelihood of complications during the birth of a baby. Not infrequently, early rupture of amniotic fluid, hypoxia and prolapse of some parts (umbilical cord, arms, legs) during attempts are observed.

The most dangerous is the re-carrying of pregnancy if narrow hips are diagnosed. Often, doctors decide to conduct a planned caesarean section to minimize the risk of serious injury.

The bone pelvis consists of a large and small pelvis. The border between them: behind - the sacral cape; from the sides - nameless lines, in front - top part pubic symphysis.

The bone base of the pelvis is made up of two pelvic bones: the sacrum and the coccyx.

The female pelvis is different from the male pelvis.

Large pelvis in obstetric practice important does not have, but it is available for measurement. By its size judge the shape and size of the small pelvis. An obstetric pelvis is used to measure the large pelvis.

Main dimensions female pelvis :

In obstetric practice, the pelvis plays a fundamental role, which consists of 4 planes:

1. The plane of the entrance to the small pelvis.
2. The plane of the wide part of the small pelvis.
3. The plane of the narrow part of the pelvic cavity.
4. The plane of exit from the small pelvis.

The plane of the entrance to the small pelvis

Borders: behind - the sacral cape, in front - the upper edge of the pubic symphysis, on the sides - nameless lines.

The direct size is the distance from the sacral cape to top edge false articulation 11 cm. The main size in obstetrics coniugata vera.

The transverse dimension is 13 cm - the distance between the most distant points of the nameless lines.

Oblique dimensions - this is the distance from the sacroiliac joint on the left to the false ledge on the right and vice versa - 12 cm.

The plane of the wide part of the small pelvis

Borders: in front - the middle of the false articulation, behind - the junction of the 2nd and 3rd sacral vertebrae, on the sides - the middle of the acetabulum.

It has 2 sizes: straight and transverse, which are equal to each other - 12.5 cm.

The direct size is the distance between the gray hair of the pubic joint and the junctions of the 2nd and 3rd sacral vertebrae.

The transverse dimension is the distance between the midpoints of the acetabulum.

The plane of the narrow part of the pelvic cavity

Borders: in front - the lower edge of the pubic symphysis, behind - the sacrococcygeal articulation, on the sides - ischial spines.

The direct size is the distance between the lower edge of the pubic joint and the sacrococcygeal joint - 11 cm.

The transverse dimension is the distance between the ischial spines - 10.5 cm.

The plane of exit from the small pelvis

Borders: in front - the lower edge of the pubic joint, behind - the tip of the coccyx, on the sides - the inner surface of the ischial tuberosities.

The direct size is the distance between the lower edge of the symphysis and the tip of the coccyx. During childbirth, the head of the fetus deviates the coccyx by 1.5-2 cm, increasing its size to 11.5 cm.

Transverse size - the distance between the ischial tubercles - 11 cm.

The angle of inclination of the pelvis is the angle formed between the horizontal plane and the plane of the entrance to the small pelvis, and is 55-60 degrees.

The wire axis of the pelvis is a line connecting the vertices of all direct dimensions of 4 planes. It has the shape of not a straight line, but concave and open in front. This is the line along which the fetus passes, being born through the birth canal.

Pelvis conjugates

External conjugate - 20 cm. Measured with a tazometer with external obstetric research.

Diagonal conjugate - 13 cm. Measured by hand during internal obstetric examination. This is the distance from the lower edge of the symphysis (inner surface) to the sacral promontory.

The true conjugate is 11 cm. This is the distance from the upper edge of the symphysis to the sacral promontory. The measurement is not available. It is calculated by the size of the outer and diagonal conjugate.

According to the external conjugate:

9 is a constant number.

20 - external conjugate.

According to the diagonal conjugate:

1.5-2 cm is the Solovyov index.

The thickness of the bone is determined along the circumference of the wrist joint. If it is 14-16 cm, then 1.5 cm is subtracted.

If 17-18 cm - 2 cm is subtracted.

Rhombus Michaelis - the formation, which is located on the back, has a diamond shape.

It has dimensions: vertical - 11 cm and horizontal - 9 cm. In total (20 cm) giving the size of the outer conjugate. Fine vertical dimension corresponds to the value of the true conjugate. The shape of the rhombus and its size are judged on the state of the small pelvis.

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Dimensions of the entrance of the pelvis.

Bone Entry Ring normal pelvis at adult woman has the shape of a transverse oval. In this oval, dimensions are distinguished that go 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 back surface) to the prominent point of the promontory of the sacrum - is 11 cm; this size is called the true conjugate (conjugata) 1.
In obstetrics, two true conjugates are distinguished (Fig. 96). The conjugate just discussed is the anatomical true conjugate; another conjugate passes to the same point of the cape 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 an 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 sacro- iliac joint on the right and left to the iliac-pubic tubercle of the opposite side; the oblique size of the entrance is 12 cm.
The conjugate is the shortest dimension of the ellipse.

There are right and left oblique dimensions (Fig. 87); the right one goes from the right sacroiliac joint to the left iliac-pubic tubercle; left oblique size - from the left sacroiliac joint to the right iliac-pubic tubercle. Thus, the directions of oblique dimensions are determined by the backsight from which they start.
It is extremely important to be well versed in this, since these directions are used to determine the position in the pelvis of the presenting part of the fetus.
In the cavity of the small pelvis, the sizes of the wide and narrow parts of it are separately distinguished.
Dimensions of the upper, or wide, part of the pelvic cavity.
The direct size goes from the middle of the posterior surface of the symphysis to the junction of the II sacral vertebra with the III sacral vertebra; it is equal to 12.5 cm.
The transverse dimension passes between the inner surfaces of the bottom of the acetabulum; it is equal to 12.5 cm.
The oblique dimensions of the wide part of the pelvic cavity are the distance from the upper edge of the large ischial notch (incisura ischiadica major) of one side to the upper edge of the obturator foramen (foramen obturatorium) of the other side. Each of these dimensions is 13 cm.
Dimensions of the lower, or narrow, part of the pelvic cavity. Direct size - from the lower edge of the symphysis to the top 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 anterior-posterior direction, approaching the standing oval.
The dimensions of the outlet of the pelvis. The direct size (Fig. 88) - the distance from the lower edge of the symphysis to the top of the coccyx - is 9 -9.5 cm. During delivery by pressure of the incoming presenting part of the fetus, the tip of the coccyx is bent backwards by 1 - 1.5 cm, why the direct exit size may increase up to 11 cm.
The transverse dimension of the exit (Fig. 88) - the distance between internal parties ischial tubercles - equal to 10.5 cm; the exit of the pelvis has the shape of a standing oval.

Thus, at the entrance of the pelvis, the largest size is transverse; in the cavity - oblique, in the exit - straight size. If you 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 looks like a transversely lying oval; descending lower, the oval gradually assumes a slightly oblique position; descending even lower, it gradually turns and in the lowest part of the lumen of the pelvic canal, at the exit of the pelvis, takes the position of a standing oval.

Rice. 88. Exit of the pelvis 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 various departments pelvic canal. We will return to this when studying the mechanism of childbirth.
Determining the true conjugate from the outer conjugate. To calculate the true conjugate from the outer conjugate, 9 cm is subtracted from the length of the outer conjugate. So, with an outer conjugate equal to 20 cm, the true conjugate is determined at 11 cm. It is clear that this calculation is approximate, since there are a number of points that make it difficult to accurately calculate, as, for example, different thicknesses of soft tissues and the bones themselves.
Determination of the true conjugate by the 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 protruding point of the promontory of the sacrum, it is necessary to make vaginal examination, observing the rules of asepsis and antisepsis (see chapter VIII).
The ends of the fingers first feel the anterior wall of the pelvis, reveal the structure of the posterior surface of the symphysis, establish whether there are bony protrusions (exostoses) that reduce the size of the pelvis, determine the approximate height of the symphysis, then feel the side walls of the pelvis and also reveal whether there are any deformations here.

Rice. 89. Diagonal conjugate measurement (first moment).

Rice. 90. Diagonal conjugate measurement (second moment).
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 course of the upcoming birth. Finally, by back wall vagina, along the sacral cavity, move up and try to reach the cape of the sacrum. In a normal pelvis, the promontory can only be reached if the examining midwife has long fingers. Usually when medium length fingers of the examiner's hand, if the cape 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 right triangle, in which one leg is a symphysis, the other is a true conjugate (Fig. 96). Having the opportunity to measure the diagonal conjugate and the height of the symphysis (Fig. 94), that is, 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 cape is reached, then, resting against it with the end of the middle finger of the investigating hand, with the end of the index finger of the other hand (Fig. 89), they mark on the investigating 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 for a babysitter or last resort measure the pregnant woman with a centimeter tape, and preferably with a tazomer (Fig. 90), the distance from the mark to the end of the middle finger - this will be the length of the diagonal conjugate. To determine the size of a true conjugate, an average of 1.5 to 2 cm is subtracted from the length of the diagonal conjugate due to the difference in length between the two conjugates.
Determining the size of the exit of the pelvis. To determine the size of this part of the pelvis, the woman is placed in a position on her back with her hips pressed against her stomach.
The direct size of the exit of the pelvis is measured from the lower edge of the symphysis to the top of the coccyx (Fig. 91).
The transverse size of the outlet is the distance between the ischial tubercles. First, the ischial tubercles are felt with their fingers, and the buttons of a special tazomer are pressed tightly against the inner surfaces of these tubercles, or this distance is measured with a centimeter tape (Fig. 92). 1-1.5 cm is added to the size obtained in this way, depending on the thickness of the subcutaneous fat layer.

Rice. 92. Measurement of the transverse size of the exit of the pelvis.
The size of the exit of the pelvis 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 tubercles are located to each other. Roughly it can be measured, as shown in Fig. 93.

Oblique dimensions of the pelvis

The asymmetry of the pelvis is determined based on the measurement of the oblique dimensions of the pelvis. To do this, compare the distances between the following points:

1. from the middle of the symphysis to the posterior superior iliac spines on the right and left (for a normal pelvis 17 cm);

Rice. 93. Measurement of the magnitude of the pubic angle

1. from the anterior-superior spine of one side to the postero-superior spine of the opposite side and vice versa (for a normal pelvis 21 cm);

3) from the spinous process V lumbar vertebra to the anterior superior spine of the right and left iliac bones (for a normal pelvis 18 cm).

Rice. 94. Determining the height of the symphysis
In a symmetrical pelvis, these paired sizes are the same; if one is larger and the other is smaller, then the pelvis is asymmetrical, oblique. The difference in the magnitude of the oblique dimensions already determines the degree of this distortion. The asymmetry of the pelvis can be judged to some extent by the shape of the lumbar rhombus (p. 357).

Measurement of 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 turn out to 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 fluctuates. To measure the height of the symphysis, a bent index finger is drawn along the back surface of the symphysis and pressed tightly to it with the palmar surface (Fig. 94). Having reached the upper edge of the symphysis with the end of the examining finger, index finger with the other hand, 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, not 1.5, but 2 cm should be subtracted from the length of the diagonal conjugate.

A large pelvis for the birth of a child is not essential. The bone base of the birth canal, which is an obstacle to the fetus being born, is the small pelvis. However, the size of the large pelvis can indirectly judge the shape and size of the small pelvis.

The planes and dimensions of the small pelvis

Entrance to the pelvic cavity
Straight size - 11 cm
Transverse size - 13-13.5 cm
Oblique size - 12-12.5 cm

Wide part of the pelvis
Straight size - 12.5 cm
Cross size - 12.5 cm
Oblique size - 13 cm (conditionally)

narrow part of the pelvis
Straight size - 11 cm
Cross size - 10.5 cm

Exit from the pelvis
Straight size - 9.5 cm
Cross size - 11 cm

pelvic cavity called the space enclosed between the walls of the pelvis, from above and below bounded by the planes of entry and exit of the pelvis. It has the form of a cylinder, truncated from front to back, and the front part, facing the bosom, is almost 3 times lower than the back, facing the sacrum. In connection with this form of the pelvic cavity, its various departments have an unequal shape and size. These sections are imaginary planes passing through the identification points of the inner surface of the small pelvis. In the small pelvis, the following planes are distinguished: the plane of entry, the plane of the wide part, the plane of the narrow part and the plane of exit. (Fig. 1)

The plane of the entrance to the small pelvis passes through the upper inner edge of the pubic arch, nameless lines and the top of the cape. In the entrance plane, the following dimensions are distinguished (Fig. 2).

• Straight size - shortest distance between the middle of the upper inner edge of the pubic arch and the most prominent point of the cape. This distance is called true conjugate(conjugata vera); it is equal to 11 cm. It is also customary to distinguish between and anatomical conjugate- distance from the middle of the upper edge of the pubic arch to the same point of the cape; it is 0.2-0.3 cm longer than the true conjugate (see Fig. 1).
• Transverse dimension- the distance between the most distant points of the nameless lines opposite sides. It is equal to 13.5 cm. This size crosses the true conjugate eccentrically at a right angle, closer to the cape.
• oblique dimensions- right and left. The right oblique size goes from the right sacroiliac joint to the left ilio-pubic tubercle, and the left oblique size goes from the left sacroiliac joint to the right ilio-pubic tubercle, respectively. Each of these dimensions is 12 cm. As can be seen from the given dimensions, the entrance plane has a transverse oval shape.

• Straight size- from the middle of the inner surface of the pubic arch to the articulation between the II and III sacral vertebrae; it is equal to 12.5 cm.
• Transverse dimension, connecting the most distant points of the plates of the acetabulum of both sides is 12.5 cm. The plane of the wide part approaches a circle in its shape.

• Straight size- from the lower edge of the pubic joint to the sacrococcygeal joint. It is equal to 11 cm.
• Transverse dimension- between inner surface ischial spines. It is equal to 10.5 cm.

• Straight size- from the middle of the lower edge of the pubic joint to the top of the coccyx. It is equal to 9.5 cm. Due to some mobility of the coccyx, the direct exit size can lengthen during childbirth when the fetal head passes by 1-2 cm and reach 11.5 cm.
• Transverse dimension between the most distant points internal surfaces ischial tubercles. It is equal to 11 cm.