What is a narrow pelvis? The dimensions of the pelvis are normal and with the main most common types of narrowing of the pelvis

Accurate determination of the size of the pelvis in obstetrics before the onset of labor can save the life of the mother and child. Every woman goes through this procedure, since with its help you can understand in advance whether it is necessary C-section. In gynecology, the sizes of the large and small pelvis are measured; each distance has its own name and standards. To carry out the procedure, a special instrument is used - a medical metal compass - a tazomer.

Basic parameters of the large pelvis

Female pelvis significantly different in size from men's. It is important for a girl to know several parameters and their meanings to make sure that doctors are acting correctly:

1. The spinarum distance is normally 25-26 cm - this is the distance between the anterosuperior spines of the bones of the iliac zone.
2. Distance cristarum – normally 28-29 cm – position of the distant capes of the ridges iliac bones located above the hip joint.
3. External conjugate - from 20 to 21 cm - the distance from the middle of the top of the symphysis to the upper corner of the Michaelis rhombus.

An awn is an acute formation on the bones, which is diagnosed both normally and with various diseases. Osteophytes and osteoporosis are derivatives of this word.

Narrowing of the female pelvis is a common problem in obstetrics. This indicator matters:

• at grade 1 - the mildest - the true conjugate retains a size greater than 9, but less than 11 cm;
• with degree 2 narrowing of the pelvis, this figure is 7 and 9 cm, respectively;
• at grade 3 – 5 and 7 cm;
• at grade 4, the true conjugate barely reaches 5 cm.

The true conjugate of the pelvis is the distance from the protruding part of the sacrum to the superior promontory of the pubic symphysis at the exit. The easiest way to determine the parameter is by the dimensions of the conjugates on the outside.

A true conjugate is the smallest distance inside through which the fetus emerges during childbirth. If the indicator is less than 10.5 cm, then doctors prohibit natural childbirth. The true conjugate parameter is established by subtracting 9 cm from the external indicator.

The diagonal conjugate is the distance from the bottom of the symphysis pubis to the prominent point of the sacrum. It is determined using vaginal diagnostics. At normal pelvis the indicator does not exceed 13 cm, sometimes it is at least 12 cm. To clarify the true conjugate, 1.5-2 cm is subtracted from the resulting figure.

When examining the diagonal indicator, the doctor in rare cases reaches with his fingers to the promontory of the sacrum. Usually, if the bone is not felt when you place your fingers inside the vagina, the size of the pelvis is considered normal.

The shape of the pelvis can affect normal indicators. With a platipeloid constitution, which occurs in 3% of women, the pelvis is elongated and slightly flattened. In this case, the gap between the bones narrows, as a result of which the birth process can be complicated.

Pelvic planes

To understand exact specifications female skeleton, it is necessary to measure the plane before childbirth:

1. Entrance plane. In front, it starts from the top of the symphysis and reaches behind the promontory, and the lateral distance is bordered by the innominate line. The direct size of the entrance corresponds to the true conjugate - 11 cm. The transverse size of 1 plane is between distant points of the boundary lines, not less than 13 cm. The oblique sizes start from the sacroiliac joint and continue to the pubic tubercle - from 12 to 12.5 cm normally. The entrance plane usually has a transverse oval shape.
2. Plane of the wide part. It runs through the inner surface of the womb strictly in the middle, passes along the sacrum and projection acetabulum. Possesses round shape. The straight size is measured, which is normally 12.5 cm. It starts from the middle of the pubic symphysis and extends to the 2nd and 3rd vertebrae of the sacrum above the buttocks. The transverse size of the zone is 12.5 cm, measured from the middle of one plate to the other.
3. Plane of the narrow part. It starts from the bottom of the symphysis and reaches behind the sacrococcygeal joint. On the sides the plane is limited by the ischial spines. The straight size is 11 cm, the transverse size is 10 cm.
4. Exit plane. It connects the lower edge of the symphysis with the edge of the coccyx at an angle, along the edges it goes into the ischia bones located in the buttocks area. The direct size is 9.5 cm (if the tailbone is deviated, then 11.5 cm), and the transverse size is 10.5 cm.

In order not to get confused in all the indicators, you can only pay attention to the measurement of the large pelvis. The table shows an additional parameter - the distance between the trochanters of the femurs.

Spit femur located at the point where girls usually measure their hip volume.

Determining the size of the pelvis: narrow or wide

By comparing the obtained indicators, it is easy to determine whether a woman has wide or narrow hips. After consulting with a gynecologist and determining whether the size of the female pelvis is normal, you can decide whether to have a caesarean section or give birth on your own.

Indicators are higher than normal

In most cases, a wide female pelvis is a good factor for pregnancy. Girls should understand that if a woman loses weight, the pelvis cannot become narrower because of this - everything is inherent in the structure of the bones. Wide hips are most often found in large women, and this cannot be considered a pathology. If the dimensions exceed the norm by 2-3 centimeters, this is considered a wide pelvis.

The main danger of too wide hips is rapid labor. In such a situation, the child passes much faster through the birth canal, which can lead to female injuries: rupture of the cervix, vagina and perineum.

Anatomically narrow pelvis

The definition of an anatomically narrow pelvis in obstetrics is closely related to normal indicators. A deviation of 1.5 cm from the minimum limit indicates that the woman has small hips. In this case, the conjugate should be less than 11 cm. Natural childbirth in this case, are possible only when the child is small.

When diagnosing, the doctor identifies the type of pelvis: transversely narrowed, uniformly narrowed, flat, simple or rachitic. Less common pathological forms, in which the pelvis began to narrow pathological changes V bone structure: kyphotic, deformed, oblique or spondylolisthetic pelvis. Causes of anatomically narrow pelvis:

• bone injuries;
• rickets;
• elevated physical exercise and lack proper nutrition in childhood;
• neoplasms in the study area;
• hyperandrogenism, leading to male type formation;
• accelerated growth during adolescence;
• psycho-emotional stress that caused compensatory development in childhood;
• general physiological or sexual infantilism;
• cerebral palsy, birth injuries, polio;
• professional sports;
• metabolic problems;
• dislocations of the hip joints;
• inflammatory or infectious diseases skeletal system;
• rachiocampsis.

Factors that provoke improper formation of the pelvis include: hormonal imbalance, constant colds and problems with the menstrual cycle.

Clinically narrow pelvis

Clinically narrow pelvis It can be detected only before childbirth, or during the process of delivery. This is due to the discrepancy between the size of the fetus and the woman’s birth canal. For example, if the child’s weight is more than 4 kg, even a girl with normal indicators. There is no single answer to the question of why this condition is formed. The doctor identifies a whole range of reasons:

• large fruit;
• post-term for more than 40 weeks;
• malposition;
• tumors of the uterus or ovaries;
• fetal hydrocephalus (enlarged head);
• fusion of the vaginal walls;
• breech presentation of the fetus (the baby is turned with the pelvis instead of the head).

In obstetric practice, there are more and more cases of clinically narrow birth canal, because large children are born.

Every woman should know her pelvic parameters before giving birth. A responsible gynecologist never ignores these indicators and carefully conducts the examination using an obstetric caliper.

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. Bonespelvis

Most important of all methods of pelvic examination has its measurement. Knowing the size of the pelvis, one can judge the course of labor, the possible complications with them, about the admissibility spontaneous labor for a given shape and size of the pelvis. Majority internal dimensions The pelvis is not available for measurement, so the external dimensions of the pelvis are usually measured and the size and shape of the small pelvis are 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.)

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

Rice. 3. Measuring spinarum distance

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

Rice. 4. Crystarum distance measurement

Triangular distance (Distantiatrochanterica D. Tr.)- the distance between the greater trochanters of the femurs. This size is 31 -32 cm (Fig. 5).

Rice. 5. Measuring the distance of the triangular

Conjugata externaС. Ext.- external conjugate, i.e. straight pelvic size. To do this, the woman is laid on her side, the underlying leg is bent at the hip and knee joints, and the overlying leg is extended. The outer conjugate is normally 20-21 cm (Fig. 6).

Rice. 6. Measuring the outer conjugate

External conjugate is important: by its size one can judge the size true conjugates- the distance between the sacral promontory - the most protruding point inside the sacrum and the most protruding point on the inner surface of the pubic symphysis (the junction of the pubic bones). This smallest size inside the pelvis through which the fetal head passes during childbirth. If the true conjugate is less than 10.5 cm, then vaginal delivery may be difficult or simply impossible; in this case, a caesarean section is often performed. To determine the true conjugate, subtract 9 cm from the length of the outer conjugate. For example, if the outer conjugate is 20 cm, then the true conjugate is 11 cm; if the outer conjugate has a length of 18 cm, then the true one is 9 cm, etc. The difference between external and true conjugates depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of bones and soft tissues in women is different, so the difference between the size of the external and true conjugate does not always exactly correspond to 9 cm. The true conjugate can be more accurately determined by the diagonal conjugate.

Diagonal conjugate (conju-gatadiagonalis) is the distance from the lower edge of the symphysis to the most prominent point of the sacral promontory. The diagonal conjugate is determined during a vaginal examination of the woman (Fig. 7). The diagonal conjugate with a normal pelvis is on average 12.5-13 cm. To determine the true conjugate, 1.5-2 cm is subtracted from the size of the diagonal conjugate.

Rice. 7. Diagonal conjugate measurement

The doctor is not always able to measure the diagonal conjugate, because when normal sizes of the pelvis 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. Pelvic dimensions and external conjugate measured in all pregnant and postpartum women 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 with her legs bent at the hips 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 it is necessary to obtain additional data on the size of the pelvis, its correspondence to the size of the fetal head, deformations of the bones and their joints, an X-ray examination of the pelvis is performed - X-ray pelviometry. Such an examination is possible at the end of the third trimester of pregnancy, when all the organs and tissues of the fetus are formed and an x-ray examination will not harm the baby. This study is carried out with the woman lying on her back and side, which makes it possible to determine the shape of the sacrum, pubic and other bones; A special ruler is used to determine the transverse and straight dimensions of the pelvis. The fetal head is also measured, and on this basis it is judged whether its size corresponds to the size of the pelvis.

The size of the pelvis and its correspondence to the size of the head can be judged from the results ultrasound examination. This study allows you to measure the size of the fetal head, determine how the fetal head is located, because in cases where the head is extended, that is, the forehead or face is presented, it requires more space than in cases where the occiput is presented. Fortunately, in most cases, birth takes place in the occipital presentation.

When measuring externally, it is difficult to take into account the thickness of the pelvic bones. Measuring a circumference with a centimeter tape is a well-known value. 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 bones of the pelvis are massive and the dimensions of its cavity are smaller than would be expected from measurements of a large pelvis. If the index is less than 14 cm, then we can say that the bones are thin, which means that even with small external dimensions The dimensions of the internal cavities are sufficient for the baby to pass through them.

The time when a narrow pelvis was a kind of death sentence for a woman in labor has long gone. Modern medicine allows you to ensure a successful outcome of childbirth, regardless of the structural features of the woman’s pelvis. But for this, doctors must carry out the necessary measurements in a timely manner. And every woman should be aware of the significance of this procedure.

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

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
Transverse size - 12.5 cm
Oblique size - 13 cm (conditionally)

Narrow part of the pelvis
Straight size - 11 cm
Transverse size - 10.5 cm

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

Pelvic cavity is the space enclosed between the walls of the pelvis, limited above and below by the planes of inlet and outlet of the pelvis. It has the appearance of a cylinder, truncated from front to back, with the front part facing the womb almost 3 times lower than the back part facing the sacrum. Due to this shape of the pelvic cavity, its various parts have different shapes and sizes. These sections are imaginary planes passing through identification points of the inner surface of the 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 exit plane. (Fig. 1)

Plane of entry into the pelvis passes through the upper inner edge of the pubic arch, the innominate lines and the apex of the promontory. In the entrance plane, the following dimensions are distinguished (Fig. 2).

• Straight size- the 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 anatomical conjugate- the distance from the middle of the upper edge of the pubic arch to the same point of the promontory; it is 0.2-0.3 cm longer than the true conjugate (see Fig. 1).
• Transverse size- the distance between the most distant points of the nameless lines of opposite sides. It is equal to 13.5 cm. This size intersects at a right angle true conjugate eccentric, closer to the cape.
• Oblique dimensions- right and left. The right oblique dimension goes from the right sacroiliac joint to the left iliopubic tubercle, and the left oblique dimension goes from the left sacroiliac joint to the right iliopubic tubercle. 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 12.5 cm.
• Transverse size, connecting the most distant points of the plates of the acetabulum of both sides is equal to 12.5 cm. The plane of the wide part in its shape approaches a circle.

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

• Straight size- from the middle of the lower edge of the symphysis pubis to the apex of the coccyx. It is equal to 9.5 cm. The direct size of the outlet, due to some mobility of the coccyx, can lengthen during childbirth when the fetal head passes by 1-2 cm and reach 11.5 cm.
• Transverse size between the most distant points of the internal surfaces of the ischial tuberosities. It is 11 cm.

FEMALE PELUS with obstetric point vision.

The bony pelvis consists of two pelvic bones, the sacrum and the coccygeal bone, which are firmly connected through cartilaginous layers and connections.

The pelvic bone is formed from the fusion of three bones: longitudinal, ischial and pubic. They connect at the acetabulum.

The sacrum consists of 5-6 motionlessly connected vertebrae that merge into one bone.

The coccygeal bone consists of 4-5 underdeveloped vertebrae.

Bone pelvis in upper section open forward. This part is called the large pelvis. Bottom part - is closed bone formation- small pelvis. The border between the large and small pelvis is the terminal (nameless) line: in front is the upper edge of the symphysis and pubic bones, on the sides - arcuate lines of the ilium, behind - the sacral prominence. The plane between the large and small pelvis is the entrance to the small pelvis. The large pelvis is much wider than the small one, it is limited on the sides by the wings of the ilium, behind by the last lumbar vertebrae, in front by lower section anterior abdominal wall.

All women have their pelvis measured. There is a relationship between the sizes of the large and small pelvis. By measuring a large pelvis, we can draw conclusions about the size of a small one.

Normal sizes of the female pelvis:

• distantia spinarum - the distance between the anterior upper bones of the longitudinal bone - 25-26 cm;
• distantia cristarum - the distance between distant points of the iliac crests - 28-29 cm;
• conjugata externa - (external conjugate) - the distance from the middle of the upper edge of the symphysis to the upper corner of the Michaelis rhombus (measurements are carried out with the woman lying on her side) - 20-21 cm.

Michaelis rhombus- this is an expansion of deepening in sacral region the limits of which are: above - the fossa under the spinous process of the fifth lumbar vertebra(supracrigian fossa), below - points corresponding to the posterosuperior spine of the iliac bones. The average length of a rhombus is 11 cm, and its diameter is 10 cm.

Diagonal conjugate— the distance from the lower edge of the symphysis to the most protruding point of the promontory of the sacral bone is determined during vaginal examination. With normal pelvic sizes it is 12.5-13 cm.

The size of the true conjugate (direct size of the entrance to the small pelvis) is determined by subtracting 9 cm from the length of the external conjugate or subtracting 1.5-2 cm from the length of the diagonal conjugate (depending on the Solovyov index).

Solovyov index - the circumference of the wrist-carpal joint, divided by 10. The index allows you to have an idea of ​​​​the thickness of a woman’s bones. The thinner the bones (index = 1.4-1.6), the more capacity small pelvis. In these cases, 1.5 cm is subtracted from the diagonal conjugate to obtain the length of the true conjugate. With the Solovyov index

I, 7-1.8 - subtract 2 cm.

Pelvic tilt angle — the angle between the plane of the entrance to the small pelvis and the horizon is 55-60 °. Deviations in one direction or another can negatively affect the course of labor.

The normal height of the symphysis is 4 cm and is measured index finger during vaginal examination.
Pubic angle - with normal pelvic sizes is 90-100 °.

Small pelvis - This is the bony part of the birth canal. Back wall The small pelvis consists of the sacrum and coccyx, the lateral ones are formed by the ischium, the anterior one is formed by the pubic bones and the symphysis. The small pelvis has the following sections: inlet, cavity and outlet.

In the pelvic cavity there are wide and narrow parts. In this regard, four planes of the pelvis are determined:

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

The plane of entry into the pelvis passes through the upper inner edge of the pubic arch, the innominate lines and the apex of the promontory. The following dimensions are distinguished in the entrance plane:

1. Direct size - the distance from the sacral protrusion to the point that most protrudes on the upper inner surface of the symphysis - this is the obstetric, or true conjugate, equal to 11 cm.
2. Transverse size is the distance between the distant points of the arcuate lines, which is 13-13.5 cm.
3. Two oblique dimensions - from the iliosacral junction on one side to the iliopubic tubercle on the opposite side of the pelvis. They are 12-12.5 cm.

The plane of the wide part of the pelvic cavity passes through the middle of the inner surface of the pubic arch, on the sides through the middle of the trochanteric cavity and behind - through the connection between the II and III sacral vertebrae.

In the plane of the wide part of the small pelvis there are:

1. Direct size - from the middle of the inner surface of the pubic arch to the junction between the II and III sacral vertebrae. It is 12.5 cm.
2. The transverse dimension runs between the middles of the acetabulum. It is 12.5 cm.

The plane of the narrow part is through the lower edge of the pubic junction, on the sides - through the gluteal spines, behind -
through the sacrococcygeal joint.

In the plane of the narrow part they are distinguished:

1. Straight size - from the lower edge of the symphysis to the sacrococcygeal joint. It is equal to II.5cm.
2. Transverse size between distant points of the inner surface of the ischial spines. It is equal to 10.5 cm.

The plane of exit from the small pelvis passes in front through the lower edge of the symphysis, from the sides - through the tops of the gluteal tuberosities, and from behind - through the crown of the coccyx.

In the plane of exit from the small pelvis there are:

1. Straight size - from the tip of the coccyx to the lower edge of the symphysis. It is equal to 9.5 cm, and when the fetus passes through the pelvis it increases by 1.5-2 cm due to the deviation of the apex of the coccyx of the presenting part of the fetus.

2. Transverse size - between distant points of the internal surfaces of the ischial tuberosities; it is equal to 11cm.

The line connecting the midpoints of the straight dimensions of all planes of the pelvis is called the leading axis of the pelvis, and has the shape of a concave line forward. It is along this line that the leading point passes through the birth canal.

The main differences between the female and male pelvis:

• The bones of the female pelvis are thin and smooth;
• The female pelvis is relatively wider, lower and larger in volume;
• The wings of the ilium in women are more developed, so transverse dimensions the female pelvis is larger than the male pelvis;
• The entrance to the pelvis of a woman has a transverse oval shape, and in men it has the shape of a card heart;
• The entrance to the small pelvis in women is larger and the pelvic cavity does not narrow downward into a funnel-shaped cavity, as in men;
• The pubic angle in women is obtuse (90-100°), and in men it is acute (70-75°);
• The pelvic tilt angle in women is greater (55-60°) than in men (45°).

There are two sections of the pelvis: the large pelvis and the small pelvis. The boundary between them is the plane of the entrance to the small pelvis.

The large pelvis is bounded laterally by the wings of the ilium, and posteriorly by the last lumbar vertebra. In front it has no bony walls.

The small pelvis is of greatest importance in obstetrics. The birth of the fetus occurs through the small pelvis. There are no simple ways to measure the pelvis. At the same time, the dimensions of the large pelvis are easy to determine, and on their basis one can judge the shape and size of the small pelvis.

The pelvis is the bony part of the birth canal. The shape and size of the small pelvis are very great importance during labor and determining the tactics for its management. With sharp degrees of narrowing of the pelvis and its deformations, childbirth through the natural birth canal becomes impossible, and the woman is delivered by cesarean section.

The posterior wall of the pelvis is made up of the sacrum and coccyx, the lateral ones are the ischial bones, and the anterior wall is made up of the pubic bones with the pubic symphysis. Top part The pelvis is a continuous bony ring. In the middle and lower thirds the walls of the small pelvis are not solid. In the lateral sections there are greater and lesser sciatic foramina, bounded respectively by the greater and lesser sciatic notches and ligaments. The branches of the pubic and ischial bones, merging, surround the obturator foramen, which has the shape of a triangle with rounded corners.

In the small pelvis there are an entrance, a cavity and an exit. In the pelvic cavity there are wide and narrow parts. In accordance with this, four classic planes are distinguished in the small pelvis.

The plane of entrance to the small pelvis is limited in front by the upper edge of the symphysis and the upper inner edge of the pubic bones, on the sides by the arcuate lines of the ilium and behind by the sacral promontory. This plane has the shape of a transverse oval (or kidney-shaped). It has three sizes: straight, transverse and 2 oblique (right and left). The direct dimension is the distance from the superior inner edge of the symphysis to the sacral promontory. This size is called the true or obstetric conjugate and is equal to 11 cm.

In the plane of the entrance to the small pelvis, an anatomical conjugate is also distinguished - the distance between the upper edge of the symphysis and the sacral promontory. The size of the anatomical conjugate is 11.5 cm. The transverse size is the distance between the most distant sections of the arcuate lines. It is 13.0-13.5 cm.

The oblique dimensions of the plane of entrance to the small pelvis are the distance between the sacroiliac joint of one side and the iliopubic eminence of the opposite side. The right oblique size is determined from the right sacroiliac joint, the left - from the left. These sizes range from 12.0 to 12.5 cm.

The plane of the wide part of the pelvic cavity is limited in front by the middle of the inner surface of the symphysis, on the sides by the middle of the plates covering the acetabulum, and behind by the junction of the II and III sacral vertebrae. In the wide part of the pelvic cavity there are 2 sizes: straight and transverse.

Direct size - the distance between the junction of the II and III sacral vertebrae and the middle of the inner surface of the symphysis. It is 12.5 cm.

Transverse size is the distance between the middles of the internal surfaces of the plates covering the acetabulum. It is equal to 12.5 cm. Since the pelvis in the wide part of the cavity does not represent a continuous bone ring, oblique dimensions in this section are allowed only conditionally (13 cm each).

The plane of the narrow part of the pelvic cavity is limited in front by the lower edge of the symphysis, on the sides by the spines of the ischial bones, and behind by the sacrococcygeal joint. In this plane there are also 2 sizes.

Straight size - the distance between the lower edge of the symphysis and the sacrococcygeal joint. It is equal to 11.5 cm.

Transverse size - the distance between the spines of the ischial bones. It is 10.5 cm.

The plane of exit from the pelvis is limited in front by the lower edge pubic symphysis, from the sides - by the ischial tuberosities, from behind - by the tip of the coccyx.

Straight size - the distance between the lower edge of the symphysis and the tip of the coccyx. It is equal to 9.5 cm. When the fetus passes through the birth canal (through the plane of exit from the pelvis), due to the posterior movement of the coccyx, this size increases by 1.5-2.0 cm and becomes equal to 11.0-11.5 cm .

Transverse size - the distance between the inner surfaces of the ischial tuberosities. It is equal to 11.0 cm.

When comparing the sizes of the small pelvis in different planes, it turns out that in the plane of the entrance to the small pelvis the transverse dimensions are maximum, in the wide part of the pelvic cavity the direct and transverse dimensions are equal, and in the narrow part of the cavity and in the plane of the exit from the small pelvis the direct dimensions are greater than the transverse ones .

In obstetrics, in some cases, the system of parallel Goji planes is used. The first, or upper, plane (terminal) passes through the upper edge of the symphysis and the border (terminal) line. The second parallel plane is called the main plane and runs through the lower edge of the symphysis parallel to the first. The fetal head, having passed through this plane, does not subsequently encounter significant obstacles, since it has passed through a solid bone ring. The third parallel plane is the spinal plane. It runs parallel to the previous two through the spines of the ischial bones. The fourth plane, the exit plane, runs parallel to the previous three through the apex of the coccyx.

All classic planes of the pelvis converge anteriorly (symphysis) and fan out posteriorly. If you connect the midpoints of all straight dimensions of the small pelvis, you will get a line curved in the shape of a fishhook, which is called the wire axis of the pelvis. It bends in the pelvic cavity according to the concavity of the inner surface of the sacrum. The movement of the fetus along the birth canal occurs in the direction of the pelvic axis.

The pelvic inclination angle is the angle formed by the plane of the entrance to the pelvis and the horizon line. The angle of inclination of the pelvis changes as the center of gravity of the body moves. In non-pregnant women, the pelvic inclination angle is on average 45-46°, and lumbar lordosis is 4.6 cm (according to Sh. Ya. Mikeladze).

As pregnancy progresses, lumbar lordosis increases due to a shift in the center of gravity from the area of ​​the II sacral vertebra anteriorly, which leads to an increase in the angle of inclination of the pelvis.