Pelvic measurement. What size of the pelvis is considered normal for childbirth

The study of the pelvis is important in obstetrics because its structure and size have a decisive influence on the course and outcome of childbirth. A normal pelvis is one of the main conditions for the correct course of childbirth. Deviations in the structure of the pelvis, especially a decrease in its size, complicate the course of childbirth or present insurmountable obstacles to them. The study of the pelvis is carried out by inspection, palpation and measurement of its size. On examination, attention is paid to the entire pelvic area, but the lumbosacral rhombus (Michaelis rhombus) is of particular importance. The rhombus of Michaelis is called the outlines in the region of the sacrum, which have the contours of a diamond-shaped area. The upper corner of the rhombus corresponds to the spinous process of the 5th lumbar vertebra, the lower one corresponds to the top of the sacrum (the place where the gluteus maximus muscles originate), the lateral corners correspond to the superior posterior iliac spines. Based on the shape and size of the rhombus, it is possible to assess the structure of the bone pelvis, to detect its narrowing or deformation, which is of great importance in the management of childbirth. With a normal pelvis, the rhombus corresponds to the shape of a square. Its dimensions: the horizontal diagonal of the rhombus is 10-11 cm, the vertical one is 11 cm. With different narrowing of the pelvis, the horizontal and vertical diagonals will be of different sizes, as a result of which the shape of the rhombus will change.

In an external obstetric examination, measurements are made with a measuring tape (the circumference of the wrist joint, the dimensions of the Michaelis rhombus, the circumference of the abdomen and the height of the fundus of the uterus above the womb) and an obstetric compass (tazomer) in order to determine the size of the pelvis and its shape.

With a centimeter tape measure the largest circumference of the abdomen at the level of the navel (at the end of pregnancy it is 90-100 cm) and the height of the fundus of the uterus - the distance between the upper edge of the pubic joint and the fundus of the uterus. At the end of pregnancy, the height of the fundus of the uterus is 32-34 cm. Measuring the abdomen and the height of the fundus of the uterus above the womb allows the obstetrician to determine the gestational age, the estimated weight of the fetus, to identify disorders of fat metabolism, polyhydramnios, and multiple pregnancies. By the external dimensions of the large pelvis, one can judge the size and shape of the small pelvis. The pelvis is measured with a tazometer. Only some measurements (exit of the pelvis and additional measurements) can be made with a centimeter tape. Usually four sizes of the pelvis are measured - three transverse and one straight. The subject is in the supine position, the obstetrician sits to the side of her and facing her. Distantia spinarum - the distance between the most distant points of the anterior superior iliac spines (spina iliaca anterior superior) is 25-26 cm. Distantia cristarum - the distance between the most distant points of the iliac crests (crista ossis ilei) is 28-29 cm. Distantia trochanterica - the distance between the large trochanters of the femur (trochanter major) is 31-32 cm. Conjugata externa (external conjugate) - the distance between the spinous process of the V lumbar vertebra and the upper edge of the pubic symphysis is 20-21 cm. To measure the external conjugate, the subject turns on its side, bends the underlying leg at the hip and knee joints, and extends the overlying leg. The tazomer button is placed between the spinous process of the 5th lumbar and 1st sacral vertebrae (suprasacral fossa) behind and in the middle of the upper edge of the pubic joint in front. The size of the outer conjugate can be used to judge the size of the true conjugate. The difference between the external and true conjugate 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. To characterize the thickness of the bones, the measurement of the circumference of the wrist joint and the Solovyov index (1/10 of the circumference of the wrist joint) is used. Bones are considered thin if the circumference of the wrist joint is up to 14 cm and thick if the circumference of the wrist joint is more than 14 cm. Depending on the thickness of the bones, with the same external dimensions of the pelvis, its internal dimensions may be different. For example, with an external conjugate of 20 cm and a Solovyov circumference of 12 cm (Soloviev's index is 1.2), subtract 8 cm from 20 cm and get the value of the true conjugate - 12 cm. With a Solovyov circumference of 14 cm, subtract 9 cm from 20 cm, and subtract 10 cm for 16 cm, - the true conjugate will be equal to 9 and 10 cm, respectively. The size of the true conjugate can be judged by the vertical size of the sacral rhombus and the size of Frank. The true conjugate can be more accurately determined by the diagonal conjugate. The 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 (13 cm). The diagonal conjugate is determined by a vaginal examination of a woman, which is performed with one hand. The direct size of the exit of the pelvis is the distance between the middle of the lower edge of the pubic joint and the top of the coccyx. During the examination, the pregnant woman lies on her back with her legs divorced and half-bent at the hip and knee joints. The measurement is carried out with a tazometer. This size, equal to 11 cm, is 1.5 cm larger than the true one due to the thickness of the soft tissues. Therefore, it is necessary to subtract 1.5 cm from the obtained figure 11 cm, we get the direct size of the exit from the cavity of the small pelvis, which is 9.5 cm. The transverse size of the exit of the pelvis is the distance between the inner surfaces of the ischial tubercles. The measurement is carried out with a special tazomer or centimeter tape, which are applied not directly to the ischial tuberosities, but to the tissues covering them; therefore, to the obtained dimensions of 9-9.5 cm, it is necessary to add 1.5-2 cm (soft tissue thickness). Normally, the transverse dimension is 11 cm. It is determined in the position of the pregnant woman on her back, she presses her legs to the stomach as much as possible. The oblique dimensions of the pelvis have to be measured with oblique pelvises. To identify the asymmetry of the pelvis, the following oblique dimensions are measured: the distance from the anteroposterior spine of one side to the posterior superior spine of the other side (21 cm); from the middle of the upper edge of the symphysis to the right and left posterior superior spines (17.5 cm) and from the supracross fossa to the right and left anteroposterior spines (18 cm). The oblique dimensions of one side are compared with the corresponding oblique dimensions of the other. With a normal structure of the pelvis, the size of the paired oblique dimensions is the same. A difference greater than 1 cm indicates an asymmetric pelvis. Lateral dimensions of the pelvis - the distance between the anteroposterior and posterior superior iliac spines of the same side (14 cm), measure it with a pelvis meter. Lateral dimensions must be symmetrical and not less than 14 cm. With a lateral conjugate of 12.5 cm, childbirth is impossible. The angle of inclination of the pelvis is the angle between the plane of the entrance to the pelvis and the plane of the horizon. In the standing position of a pregnant woman, it is 45-50. It is determined using a special device - a tazouglomer.

During vaginal examination, the diagonal conjugate is measured (12.5-13 cm). Obstetric conjugate - c. vera (subtract 2 cm from the dimensions of the diagonal conjugate).

The true conjugate is calculated:

along the diagonal conjunct;

by external conjugate;

according to the vertical dimension of the Michaelis rhombus;

using X-ray pelviometry;

according to ultrasound.

The capacity of the small pelvis depends on the thickness of its bones, which is indirectly determined by measuring the circumference of the wrist joint with the calculation of the Solovyov index (13.5-15.5 cm).

Rhombus Michaelis (normal - 11 x 10 cm).

The direct size of the exit of the small pelvis (9.5 cm).

The transverse size of the outlet of the small pelvis (11 cm).

The pubic angle (90 0 -100 0).

External oblique dimensions of the pelvis.

Lateral conjugate (distance between the anterior and posterior superior iliac spines on one side) - 15 cm.

Distance from the anterior-superior spine on one side to the postero-superior spine on the other side (21-22 cm).

Distance from the middle of the upper edge of the symphysis to the postero-superior spines on the right and left (17.5 cm); the difference in size indicates the asymmetry of the pelvis.

Distance from the supra-sacral fossa to the anterior-superior spines on both sides.

Pelvic circumference at the level of the iliac crests (85 cm); the same at the level of large skewers (90 - 95 cm).

The height of the fundus of the uterus; abdominal circumference.

Fetal head diameter (12 cm).

The pubosacral size (the distance from the middle of the symphysis to the junction of the 2nd and 3rd sacral vertebrae is a point located 1 cm below the intersection of the diagonals of the Michaelis rhombus - 22 cm); a decrease in this size by 2-3 cm is accompanied by a decrease in the direct size of the wide part of the pelvic cavity.

X-ray pelviometry allows you to determine all the diameters of the small pelvis, the shape, the slope of the pelvic walls, the shape of the pubic arch, the degree of curvature and the slope of the sacrum. It is recommended to produce in 38-40 weeks. pregnancy or before the onset of labor.

Ultrasound examination - ultrasound, is used to diagnose an anatomically narrow pelvis and makes it possible to obtain the value of the true conjugate and the biparietal size of the fetal head, their ratio.

The course of pregnancy and childbirth with a narrow pelvis

A narrow pelvis as such does not lead to a change in the course of pregnancy.

The adverse effect of the narrowed pelvis on the course of pregnancy affects its last months and at the beginning of childbirth.

Features that an obstetrician should know about:

In primiparas, due to a discrepancy between the pelvis and the head, the latter does not enter the pelvis and remains mobile over the entrance throughout pregnancy and at the beginning of childbirth. The height of the fundus of the uterus on the eve of childbirth remains at the same level.

In nulliparous women with a narrow pelvis, by the end of pregnancy, the abdomen has a pointed shape, and in multiparous women it is pendulous.

Anomalies of the bone pelvis are common causes of malposition of the fetus - oblique, transverse and pelvic presentation of the fetus, as well as unfavorable insertion of the head - extensor.

One of the frequent and serious complications of pregnancy with a narrow pelvis is premature (prenatal) outflow of water. This is due to the lack of a contact belt - the head stands high, it does not touch the pelvic ring, so the waters are not divided into anterior and posterior - the entire mass is poured out at the beginning of labor under increasing uterine pressure.

With the outflow of amniotic fluid and the moving head of the fetus, there is a high risk of prolapse of the umbilical cord and small parts of the fetus. Prolapse of the umbilical cord leads to the development of acute hypoxia of the fetus and its death if the head presses it against the pelvic wall. In these cases, only an emergency caesarean section can save the child (intranatal mortality among newborns in these cases is 60-70%).

With a narrow pelvis, childbirth is often complicated by the weakness of labor. Firstly, women with a narrow pelvis have hormonal insufficiency, sexual infantilism, and secondly, childbirth is protracted, which leads to fatigue of the woman in labor, depletion of energy resources and the development of secondary weakness of labor activity.

Maternal trauma. Prolonged compression of the fetal head of the bladder and rectum can lead to the formation of genitourinary and enterogenital fistulas (for 6-7 days). Compression of the cervix can lead to edema, necrosis, deep tears.

The lack of forward movement of the fetus with continued intensive labor activity leads to a gradual thinning of the lower segment and the occurrence of a threatening rupture of the uterus.

With a protracted course of childbirth with a long anhydrous interval significantly increases the risk of endometritis, chorioamnionitis, ascending infection of the fetus.

Fetal complications. The fetal head configures slowly, lingers for a long time in various planes of the small pelvis, which causes a violation of cerebral circulation, edema, an increase in the volume of the head, the formation of cephalohematomas, subdural and subarachnoid hemorrhages. With the further development of the child in these areas, a cicatricial adhesive process is formed, leading to the occurrence of deviations in the neuropsychic sphere and physical development up to the development of hydrocephalus, hyperkinesis, epilepsy and dementia. Moreover, with deep, irreversible violations of brain function, cerebral palsy can form.

Pelvic measurement is mandatory for all pregnant women. This is a quick, painless and absolutely harmless procedure, the implementation of which is an indispensable condition for issuing a pregnant card at the first visit of a woman to a gynecologist. Focusing on, you can plan the management of childbirth: naturally or surgically (caesarean section). A timely chosen tactic avoids many complications that pose a threat to the life of a woman and her baby. Properly planned childbirth is a guarantee that the birth of a child will be easy and safe.

The true conjugate is the shortest distance between the cape and the most prominent point in the pelvic cavity on the inner surface of the symphysis. Normally, this distance is 11 cm.

What's happened

The pelvis as an anatomical formation is represented by two pelvic bones and the distal spine (sacrum and coccyx). In obstetrics, only that part of it, which is called the small pelvis, is important. This is the space bounded by the lower sections of the sacrum and coccyx. It contains the following organs: bladder, uterus and rectum. In its structure, four main planes are distinguished. Each of them has several sizes that are important in obstetric practice.

Parameters of entry into the small pelvis

1. Straight size. This indicator has other names - the obstetric conjugate and the true conjugate. Equal to 110 mm.
2. Cross size. Equal to 130-135 mm.
3. The sizes are oblique. Equal 120-125 mm.
4. Diagonal conjugate. Equal to 130 mm.

Parameters of the wide part of the small pelvis

1. Straight size. Equal to 125 mm.
2. Cross size. Equal to 125 mm.

Parameters of the narrow part of the small pelvis

Pelvic exit parameters

1. Straight size. During childbirth, it can increase, as the head of the fetus moving along the birth canal bends the coccyx backwards. It is 95-115 mm.
2. Cross size. Equal to 110 mm.

Measurement of the pelvis of a pregnant woman

The above indicators are anatomical, that is, they can be determined directly from the pelvic bones. It is not possible to measure them on a living person. Therefore, in obstetric practice, the following parameters are the most important:

1. The distance between the awns located at the front edge of the ridge.
2. The distance between the points of the iliac crests that are at the maximum distance from each other.
3. The distance between the protrusions of the femurs in the area of ​​​​the transition of their upper part to the neck.
4. (distance from to the lumbosacral cavity).

Thus, the normal dimensions of the pelvis are 250-260, 280-290, 300-320 and 200-210 millimeters, respectively.

Clarification of these parameters is mandatory when registering a pregnant woman. The measurement is carried out with a special tool (tazomer), which, by the way, can also be used to measure the head of a newborn baby.

It is important to understand that the volume of soft tissues does not affect the result of the study. The parameters of the pelvis are evaluated by bone protrusions, and they do not shift anywhere when losing weight or, on the contrary, gaining weight. The dimensions of the pelvis remain unchanged after a woman reaches the age when bone growth stops.

For the diagnosis of narrowing of the pelvis, two more conjugates are important - true (obstetric) and diagonal. However, it is not possible to directly measure them; one can judge their size only indirectly. Diagonal conjugate in obstetrics is usually not measured at all. More attention is paid to the obstetric conjugate.

The determination of the true conjugate is carried out according to the formula: the value of the outer conjugate minus 9 centimeters.

What is a narrow pelvis?

Before talking about the definition of this term, it should be noted that there are two types of narrow pelvis - anatomical and clinical. These concepts, although not identical, are closely related.

An anatomically narrow pelvis should be spoken of when at least one of the parameters is smaller than the normal size of the pelvis. The degrees of narrowing are distinguished when the true conjugate is less than the norm:

• by 15-20 mm.
• 20-35 mm.
• 35-45 mm.
• more than 45 mm.

The last two degrees indicate the need for surgical intervention. The conjugate true of the 1st-2nd degree allows the possibility of continuing childbirth in a natural way, provided that there is no threat of such a condition as a clinically narrow pelvis.

A clinically narrow pelvis is a situation where the parameters of the fetal head do not match the parameters of the mother's pelvis. Moreover, all sizes of the latter can be within the normal range (that is, from the point of view of anatomy, this pelvis is not always narrow). There may also be a reverse situation, when an anatomically narrow pelvis fully corresponds to the configuration of the fetal head (for example, if the child is not large), and in this case there is no question of the diagnosis of a clinically narrow pelvis.

The main reasons for this condition:

1. On the mother's side: anatomically small pelvis, irregular shape of the pelvis (for example, deformity after injury).
2. On the part of the fetus: hydrocephalus, large size, tilting of the head when the fetus enters the small pelvis.

Depending on how pronounced the difference between the parameters of the mother's pelvis and the fetal head, there are three degrees of a clinically narrow pelvis:

1. Relative inconsistency. In this case, independent childbirth is possible, but the doctor must be ready to make a decision on surgical intervention in a timely manner.
2. Significant discrepancy.
3. Absolute mismatch.

Childbirth with a clinically narrow pelvis

The second and third degrees are indications for surgical intervention. Independent childbirth in this situation is impossible. The fetus can only be removed by performing a caesarean section.

With a relative discrepancy, childbirth in a natural way is permissible. However, one should be aware of the danger of changing the situation for the worse. The doctor should take the question of the severity of the discrepancy even during the period of contractions in order to determine in a timely manner the further tactics. Delayed diagnosis of conditions when delivery should only be performed surgically can lead to serious difficulties in removing the fetal head. With a pronounced discrepancy, the latter will be driven into the pelvic cavity by the contracting uterus, which will lead to severe head injury and death. In advanced cases, it is impossible to extract the fetus alive from the pelvic cavity even when performing a caesarean section. In such cases, childbirth has to end with a fruit-destroying operation.

Summing up

It is necessary to know the size of the pelvis. This is necessary in order to promptly suspect such pathological conditions as an anatomically and clinically narrow pelvis. The reduction in normal size can be of varying degrees of severity. In some cases, even independent childbirth is possible, in other situations it becomes necessary to perform a caesarean section.

A clinically narrow pelvis is a very insidious condition. It is not always combined with the concept of an anatomically narrow pelvis. The latter may have normal parameters, but the possibility of discrepancy between the size of the head and the size of the pelvis still exists. The occurrence of such a situation during childbirth can cause dangerous complications (first of all, the fetus will suffer). Therefore, timely diagnosis and a quick decision on further tactics are so important.

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 - the upper part of the 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.

The large pelvis in obstetric practice is not important, 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 female pelvic dimensions:

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 promontory to the upper edge of the false articulation 11 cm. The main size in obstetrics is 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 joint, 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 during external obstetric examination.

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. Normally, the vertical size corresponds to the size of the true conjugate. The shape of the rhombus and its size are judged on the state of the small pelvis.

During pregnancy, the size of the pelvis plays an important role. Sometimes the course of childbirth depends on this. If the pelvic bones are narrow, then complications may occur during childbirth or they may end in a caesarean section. A narrow pelvis is observed in about 3% of women during pregnancy, but it is not always an indicator for caesarean.

When registering for pregnancy, the female pelvis is given special attention. After measuring it, the gynecologist at the very beginning of pregnancy will be able to guess how the birth will proceed.

Distinguish anatomical And clinical narrow pelvis during pregnancy.

Anatomical narrow pelvis- discrepancy of at least one parameter by 1.5-2 cm or more from normal. It is a consequence of the impact of certain factors on the body in childhood: malnutrition, frequent infectious diseases, lack of vitamins, hormonal disorders during puberty, congenital anomalies, injuries and fractures. Also, deformation of the pelvic bones can occur as a result of tuberculosis, rickets, polio.

If a pregnant woman is diagnosed with 1 degree of narrowing out of 4, then natural childbirth is quite possible. It is also possible to give birth on your own and with 2 degrees of narrowing, but subject to certain conditions, for example, if the fetus is not large. The remaining degrees (3 and 4) are always an indication for caesarean section.

Clinical narrow pelvis- mismatch of the fetal head with the parameters of the pelvis of the woman in labor, diagnosed during childbirth. In this case, the pelvis has normal physiological parameters and shape. It is considered narrow, since the fetus is quite large or incorrectly presented with the forehead or face. For this reason, the child cannot be born naturally.

Normal pelvis sizes

The measurement of the pelvis is carried out with a special instrument, a tazometer, which measures:

Additionally, it is possible to obtain data on the parameters of the pelvic bones using the following studies:

• X-ray pelviometry. This study is allowed at the end of the third trimester, when all the tissues and organs of the fetus are already formed. Thanks to the procedure, you can find out the shape of the bones and the sacrum, determine the direct and transverse dimensions of the pelvis, measure the fetal head and determine whether it corresponds to its parameters.
• Ultrasonography. On ultrasound, it is possible to determine the correspondence between the size of the fetal head and the size of the pelvic bones. The procedure also allows you to find out the location of the fetal head, since in cases of frontal or facial presentation during childbirth, it will need more space.
• Solovyov index- measurement of the circumference of the wrist joint of a woman, thanks to which it is possible to determine the thickness of the bones and determine the direct size of the cavity of the entrance to the small pelvis. Normally, the circumference of the wrist joint is 14 cm. If it is larger, then the bones are massive, if less, then they are thin. For example, with insufficient external dimensions of the pelvic bones and with a normal Soloviev index, the dimensions of the pelvic ring are sufficient for a child to pass through it.

Childbirth with a narrow pelvis and possible complications

In the antenatal clinic, all pregnant women with a narrow pelvis are on a special account. It is very important, in this case, to determine the date of birth, since it is extremely undesirable to prolong the pregnancy. A woman will be admitted to the maternity hospital in 1-2 weeks. Closer to the due date, doctors will decide on the method of delivery.

During natural childbirth with a narrow pelvis, there is a high risk of complications in the fetus (respiratory failure, oxygen starvation, birth trauma, circulatory disorders in the brain, clavicle fracture, damage to the bones of the skull and, worst of all, intrauterine death) and the mother (weak labor activity, premature discharge of amniotic fluid, postpartum infection, the threat of uterine rupture).