External dimensions of the female pelvis. Internal dimensions of the pelvis - obstetrics

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. The bony pelvis and the soft tissues lining it constitute the birth canal through which the baby is born. It is extremely important for doctors and women to know whether the birth canal is too small for the baby. This circumstance determines the possibility of childbirth through the natural birth canal. The results of the pelvic examination are included in the medical records. So that you can understand what is written on your exchange card, we will talk in detail about what the doctor does when measuring a pregnant woman’s pelvis.

Measuring the pelvis during pregnancy

The structure and size of the pelvis are crucial for the course and outcome of childbirth. Deviations in the structure of the pelvis, especially a decrease in its size, complicate the course of labor or present insurmountable obstacles to it.

The pelvis is examined by inspection, palpation and measurement. During the examination, attention is paid to the entire pelvic area, but special importance is attached to the sacral rhombus (Michaelis rhombus, Fig. 1), the shape of which, together with other data, allows us to judge the structure of the pelvis (Fig. 2).

Rice. 1. Sacral rhombus, or Michaelis rhombus

Rice. 2. Pelvic bones

The most important of all methods of examining the pelvis is its measurement. Knowing the size of the pelvis, one can judge the course of labor, possible complications during it, and the admissibility of spontaneous childbirth with a given shape and size of the pelvis. Most of the internal dimensions of the pelvis are not available for measurement, so the external dimensions of the pelvis are usually measured and the size and shape of the small pelvis can be approximately judged from them. The pelvis is measured with a special instrument - a pelvic meter. The tazomer has the shape of a compass equipped with a scale on which centimeter and half-centimeter divisions are marked. There are buttons at the ends of the branches of the tazomer; they are applied to places the distance between which is to be measured. The following pelvic sizes are usually measured: (Latin names and abbreviations are indicated in parentheses, since the sizes are indicated that way in the exchange card.)

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

Rice. 3. Measuring spinarum distance

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

Rice. 4. Crystarum distance measurement

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

Rice. 5. Measuring the distance of the triangular

External conjugate (Conjugata externaС. Ext.) - external conjugate, i.e. straight pelvic size. To do this, the woman is laid on her side, the underlying leg is bent in

hip and knee joints, the overlying one is pulled out. The external conjugate is normally 20-21 cm (Fig. 6).

Rice. 6. Measuring the outer conjugate

The external conjugate is important: by its size one can judge the size of the true conjugate - the distance between the sacral promontory - the most protruding point inside the sacrum and the most protruding point on the inner surface of the pubic symphysis (the junction of the pubic bones). This is the 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 the external and true conjugates depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of bones and soft tissues varies in women, so the difference between the size of the external and true conjugate does not always exactly correspond to 9 cm. The true conjugate can be more accurately determined by the diagonal conjugate.

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

Rice. 7. Diagonal conjugate measurement

The doctor is not always able to measure the diagonal conjugate, because with normal pelvic sizes during a vaginal examination, the promontory of the sacrum is not reached by the examiner’s finger or is difficult to palpate. If during a vaginal examination the doctor does not reach the promontory, the volume of this pelvis can be considered normal. The dimensions of the pelvis and the external conjugate are measured in all pregnant women and women in labor without exception.

If during examination of a woman there is a suspicion of narrowing of the pelvic outlet, then the size of this cavity is determined. These measurements are not mandatory, and are measured in a position in which the woman lies on her back, legs bent at the hip and knee joints, spread to the side and pulled up to the stomach.

Determining the shape of the pubic angle is important. With normal pelvic sizes it is 90-100. The shape of the pubic angle is determined by the following technique. The woman lies on her back, legs bent and pulled up to her stomach. The palmar side of the thumbs is placed close to the lower edge of the symphysis. The location of the fingers allows us to judge the angle of the pubic arch.

Additional Research

If it is necessary to obtain additional data on the size of the pelvis, its correspondence to the size of the fetal head, deformations of the bones and their joints, an X-ray examination of the pelvis is performed - X-ray pelvimetry. Such an examination is possible at the end of the third trimester of pregnancy, when all the organs and tissues of the fetus are formed and an x-ray examination will not harm the baby. This study is carried out with the woman lying on her back and side, which makes it possible to determine the shape of the sacrum, pubic and other bones; A special ruler is used to determine the transverse and straight dimensions of the pelvis. The fetal head is also measured, and on this basis it is judged whether its size corresponds to the size of the pelvis.

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

The bony pelvis is a durable container for the internal hollow organs and surrounding tissues. The woman's pelvis forms the birth canal through which the emerging fetus moves.

Differences between the female pelvis and the male pelvis begin to emerge during puberty and become distinct in adulthood.

The bones of the female pelvis are thinner, smoother and less massive than the bones of the male pelvis. The female pelvis is lower, wider and larger in volume. The sacrum in women is wider and less concave than in men. The symphysis in women is shorter and wider. The promontory of the sacrum protrudes less forward. The entrance to the small pelvis in women is more extensive and has a transverse oval shape with a notch in the area of the sacral promontory, while in men it resembles the shape of a card heart due to the sharp protrusion of the promontory. The pelvic cavity in women is more extensive and its shape approaches a cylinder, curved anteriorly. In men, the pelvic cavity is smaller, and it narrows funnel-shaped downwards. The outlet of the pelvic cavity in a woman is wider, since the distance between the ischial tuberosities is greater. The pubic angle is wider (90-100) than in men (70-75). And the tailbone protrudes anteriorly less than in the male pelvis

Thus, we can conclude that the female pelvis is more voluminous and wider, but less deep than the male pelvis.

Pelvic bones

The pelvis consists of four bones: two pelvic bones, the sacrum, and the coccyx.

Pelvic (nameless) bone (os coxae ). Until the age of 16-18, it consists of three bones connected by cartilage: iliac, ischial and pubic. After ossification, the cartilages fuse together to form the innominate bone.

Ilium ( os ilium ) has two parts: the body and the wing. The body makes up the short, thickened part of the bone and participates in the formation of the acetabulum.

Dimensions of a large pelvis

Knowing the size of the external pelvis is very important in obstetrics, since its size is used to judge the size of the small pelvis. The measurement is made with a tazometer. There are four sizes: three transverse and one straight.

Distantia spinarum- the distance between the anterosuperior iliac spines.It is usually 25-26 cm.

Distantia cristarum- the distance between the most distant points of the iliac crests. Usually it is 28-29 cm.

Distantia trochanterica -the distance between the greater trochanters of the femurs. It is 30-31 cm.

Conugata externa -external conjugate i.e. straight pelvic size. The woman is laid on her side, the underlying leg is bent at the knee and hip joints, and the overlying leg is extended. The button of one branch of the pelvis is installed in the middle of the upper outer edge of the symphysis, the other end is pressed against the suprasacral fossa, which is located between the spinous process of the 5th lumbar vertebra and the beginning of the middle sacral crest (the suprasacral fossa coincides with the upper angle of the sacral crest). Normally it is 20-21 cm .

Conugata vera -true conjugate. To determine it, it is necessary to subtract 9 from the outer conjugate, then we get the size of the true one. The difference between the true and external conjugates depends on the thickness of the sacrum, symphysis and soft tissues, so the difference does not always exactly correspond to 9 cm. Or 1.5-2 cm is subtracted from the size of the diagonal conjugate.

Conugata diagonalis -- diagonal conjugate is the distance from the lower edge of the symphysis to the most prominent point of the sacral promontory. It is determined by vaginal examination. With a normal pelvis it is 12.5-13 cm.

Taking into account the danger of breech presentation of the fetus in the mother's pelvis, timely diagnosis and hospitalization of the woman in an obstetric hospital at 35-36 weeks of pregnancy is very important. It is also very important to resolve the issue of delivery of a pregnant woman with breech, leg, breech, and transverse and oblique positions the fetus in the mother's pelvis by caesarean section. Indications for the operation of turning a fetus on a leg are: complete dilatation of the cervix and the breaking of water during examination or in a timely manner. The operation of turning the fetus on its leg is performed under deep anesthesia. Categorical contraindications for this operation are: premature, early rupture of amniotic fluid and incomplete dilatation of the cervix.

An assessment of the anatomical structure and size of the pelvis begins with a conversation, during which health problems can be clarified before pregnancy. As a rule, a narrow pelvis in women is a consequence of:

genital infantilism;
rickets;
tuberculosis;
injuries and fractures in the pelvic area.

How to determine a narrow pelvis by external data?

When assessing the musculoskeletal system Special attention pay attention to the growth of the expectant mother. Pelvic narrowing is most typical for short women (less than 160 cm) with signs of sexual immaturity: male-pattern hair growth, narrow shoulders and chest, poorly developed mammary glands, etc. Often, a decrease in the size of the pelvic cavity is indicated by curvature of the spine and limbs, insufficient mobility (ankylosis) of the knee and hip joints.

How to determine a narrow pelvis using a pelvis meter?

A pelvis meter is a device designed to measure the size of the female pelvis (pelviometry). Externally, the instrument resembles a compass with rounded ends and a centimeter scale.

To determine a narrow pelvis in a pregnant woman, the external dimensions are measured, since the internal parameters of the bony pelvis are not available for assessment.

To determine whether a woman has a narrow pelvis or not, you need to know the parameters of three transverse and one direct dimensions.

N (abbr.) - norm

Transverse dimensions:

Spinarum(the segment between the highest points of the right and left iliac bones). N 25-26 cm.
Christarum(measurement is taken between the most distant points of the right and left iliac crests). N 28-29 cm.
Trochanterica(determine the distance from the left to the right greater trochanter of the femur). When determining this transverse size, the thickness of the subcutaneous fat in the hip area should be taken into account. N 31-32 cm.

The measurement is taken in a lying position, with legs straight and arms extended along the body. When assessing the third transverse dimension, the legs must be moved and slightly bent.

IMPORTANT! Starting from the third trimester, when a woman lies on her back for a long time, the pregnant uterus puts pressure on the vessels, disrupting venous outflow and provoking the appearance of compression syndrome of the inferior vena cava. This fact should be taken into account when performing pelviometry.

Straight size:

The external conjugate (externa) is the segment between the suprasacral fossa and the highest point of the pubic symphysis. N 20-21 cm.

To measure the external conjugate, the pregnant woman is placed on her side as follows: the underlying leg should be bent at the hip and knee joints, the upper leg should be straightened.

How to determine a narrow pelvis based on the obtained numbers?

A woman is said to have a narrowing of the pelvis if one or more external dimensions are 1.5 cm or more less than normal.

IMPORTANT! Compliance of external dimensions with the norm does not guarantee the absence of a narrow pelvis in a woman. When assessing the data, one should take into account the massiveness of the bones and the thickness of the subcutaneous fat. The option when a woman with outwardly wide hips has a narrow pelvis is quite acceptable.

How to determine a narrow pelvis by internal dimensions?

An important indicator when determining a narrow pelvis is the true conjugate. This is the internal size of the entrance to the narrow part of the pelvic ring, which is the gap between the most protruding point of the sacral promontory and the junction of the pubic bones.

The true conjugate plays an important role during the passage of the child through the birth canal, as it is the narrowest place in the pelvic cavity. N – not less than 11 cm.

During a bimanual examination, the diagonal conjugate is assessed, namely, the distance from the highest point of the sacral promontory to the lower edge of the symphysis pubis. During a vaginal examination, the tip of the doctor’s middle finger rests on the top of the promontory, and the edge of the palm rests on the edge of the symphysis pubis.

As a rule, with a diagonal conjugate of 12.5-13 cm, the fetal head moves freely along the birth canal.

To calculate the true conjugate, you need to know the outer or diagonal conjugate.

True conjugate = external conjugate minus 8-9 cm or diagonal conjugate minus 1.5-2 cm.

IMPORTANT! When determining a narrow pelvis, the following is also assessed:

direct exit size: the segment between the lower edge of the pubic bone and the coccyx (N 11 cm);
transverse size of the outlet: after palpation of the ischial tuberosities, measure the distance between them (N 9.5 cm).

How to determine a narrow pelvis using additional measurements?

Michaelis rhombus.

It is a diamond-shaped area in the lumbosacral region. The upper corner of the rhombus is the base of the sacrum, the lateral corners are the posterosuperior iliac spines, and the lower corner is the apex of the sacrum.

N of the Michaelis rhombus: longitudinal size 11 cm, transverse - 10 cm.

The vertical size of the lumbosacral rhombus normally corresponds to the true conjugate.

Solovyov index.

You can determine a narrow pelvis using a measuring tape by measuring the circumference of your wrist. In N, the Solovyov index is 14-15 cm.

A wrist thickness of more than 15 cm indicates that a woman’s bones are massive, which means that the pelvic cavity will be smaller.

Pubic symphysis.

The womb is considered to be the space between the upper and lower edges of the symphysis. In N, the height of the pubis is 4-5 cm.

If the height of the pubic symphysis is 7 cm or more, natural childbirth is impossible.

How to determine a narrow pelvis by the shape of the angle of the pubic joint?

In N, the pubic angle is obtuse (from 90 to 110°), therefore, any deviation indicates an abnormal structure of the female pelvis.

How to determine a narrow pelvis during childbirth?

If the size of the child’s head does not correspond to the size of the pelvic cavity, they speak of a clinically (functionally) narrow pelvis. This complication makes it impossible to give birth to a child through the birth canal.

A clinically narrow pelvis can be identified by Vasten’s sign: determining the elevation of the fetal head above the womb.

Insertion of the fetal head into the small pelvis occurs when the cervix is fully dilated. With a narrow pelvis, the advancement of the child is difficult, which means that Vasten’s sign will be positive (the fetal head protrudes above the womb).

IMPORTANT! Most foreign experts have come to the conclusion that determining the size of the pelvis does not provide any information when determining delivery tactics. Even with the use of additional methods such as computed tomography (CT) and bone radiography, the findings of pelvic narrowing do not constitute a basis for a planned cesarean section.

Assessment of the lengths of bone landmarks is a necessary diagnostic procedure performed by a specialist on all women during pregnancy.

The boundaries and structural features of the pelvic apparatus have been assessed in expectant mothers for many centuries. Such a simple and informative study allows doctors to obtain a lot of the diagnostic information they need.

A little about anatomy

The pelvis is a bone formation. Quite a few different bones and joints are involved in its formation. The pelvic bone apparatus is a complex architectural element. Each woman has her own characteristics of his anatomy.

The pelvic bone apparatus is formed by several bones at once: a pair of pelvic bones, the sacral bone and the coccygeal bone. Each pelvic bone in turn consists of three more: the iliac, ischial and pubic. They are connected to each other using cartilage tissue.

During pregnancy, this structure is functionally advantageous. It helps the baby move calmly through the birth canal.

The pelvis is a kind of container for the reproductive organs. During pregnancy and birth of a child, it has a very important function. It is in it that the birth canal passes, along which the baby subsequently moves during his birth.

Determining the size of this bone apparatus is very important. It is especially important to do this if the baby is not physiologically located in the mother’s womb. The breech presentation of the child with a narrow or asymmetrical pelvis of the mother requires more careful attention to the woman during her pregnancy.

Determination of clinical parameters

For many years now, doctors have been performing external examination of the pelvis in different ways. The first of them is determining pelvic parameters by palpation. The second method is to determine the lengths being studied using a special device - a tazometer.

Doctors perform this diagnostic procedure when carrying a baby. at least twice. For the first time, these clinical indicators are determined at the very beginning of pregnancy. The obtained values must be included in the pregnant woman’s personal medical record. Typically, pelvic measurements are performed on women who are registered for pregnancy.

Also, doctors determine the size of the pelvic bone apparatus in expectant mothers closer to childbirth. This is a very important prognostic indicator that allows you to assess how the birth will proceed. It also helps doctors choose the optimal method of obstetric care needed for a particular patient.

When conducting a study, the doctor will be especially interested in a special anatomical zone - Michaelis rhombus. This area is located in the lumbosacral segment of the spine.

Its changes are a very important diagnostic criterion for doctors.

The size of the pelvis is measured by an obstetrician-gynecologist, who will subsequently monitor the woman for 9 months of bearing her baby. The study is carried out in a regular office.

The pelvis is measured while the expectant mother is lying on the couch. The starting position of a pregnant woman is on her back. In order to simplify the diagnostic procedure, the expectant mother should lift her clothes from the area being measured. To determine the indicators, the doctor uses a pelvic meter.

How is the norm determined?

An obstetrician-gynecologist measures several sizes at once. One of them is longitudinal. And the other three are transverse. Each of these values has its own norm criteria. They are used by doctors to accurately determine the type of structure of the pelvic apparatus in a particular patient.

Several of the studied parameters are called a special term - Distantia or D for short. To determine the first of them, doctors measure the distance between both trochanteric areas of the thighs. They call this parameter D. trochanterica. For most women, its value is in the range from 28 to 33 cm.

To determine the next parameter under study, the distance between the crests of the iliac ossicles is determined. It is called D. cristarum. Its normal values range from 24 to 27 cm.

Another no less important determined indicator is the external conjugate. To determine it, doctors measure the distance from the upper part of the womb to the edge of the final part of the lower back (at the level of the fifth vertebra). Its values range from 20 to 21 cm.

After the measurement, the doctor can calculate true conjugate. This indicator is 9 cm less than the external one.

In medical practice, there is another method for determining this size. To do this, the doctor must determine the diagonal measurement. For this purpose, he measures the distance between the most prominent point of the sacral promontory to the lower edge of the symphysis.

More often, this clinical indicator is determined during a palpation examination by a gynecologist in the chair. Its norm is 10-13 cm.

The doctor may also take a direct measurement of the pelvic outlet. To do this, measure the distance from the top of the coccygeal bone to the lower angle of the pubis. This figure is equal to eleven centimeters.

To clarify this parameter, another refined criterion is also used - true direct metering. His norm is already nine and a half centimeters. The mathematical difference between these two defined sizes is, as a rule, one and a half centimeters.

Pelvic tilt angle is also a very important clinical indicator. Two planes, horizontal and vertical, are involved in its formation. To determine this clinical criterion, a pelvic angle gauge is used. In a vertical position, the normal values of this determined parameter are 45-50 degrees.

During the examination, the doctor may also additionally determine several other sizes. They have additional diagnostic value. Usually they are necessary to identify the individual structural features of the bone apparatus that a particular patient has.

If, when determining the size of the pelvis, a specialist identifies any asymmetry, he will also additionally measure the following parameters. They are presented in the table below:

Clinical options

The doctor takes into account the ratio of all these indicators. This allows him to assess the type of pelvis in a pregnant woman. To do this, several sizes are assessed at once: the specialist does not make a conclusion based on just one clinical parameter.

The table below shows the different types of pelvic structure in women:

How are the obtained values deciphered?

If the pelvis has a normal structure, then the Michaelis diamond looks like an inverted square. Its diagonal is about 11 cm.

When measuring this indicator, it happens that the sides of the square begin to shift. This also leads to a change in its shape: it becomes more elongated. If, when measuring, the doctor determines a pair of acute and a pair of obtuse angles, then in this case this means the presence of a narrow pelvic bone apparatus.

A wide pelvis is most often found in fairly tall and large women. This is influenced by the structural features of the musculoskeletal system of the expectant mother. Also, a wide pelvis can occur in women with an average build. In petite ladies and expectant mothers who are short in stature, this structure is practically never found.

A wide pelvis is characterized by an increase in all defined dimensions. When measuring sizes, it is very important to exclude the influence of a large amount of subcutaneous fat. For this exception, a gynecological examination is performed on a chair. By determining the true conjugate, the doctor can determine How truly wide is the pelvis of a particular patient.

Many expectant mothers think that the larger and wider the pelvic bones, the easier it will be for them to give birth on their own. This is not entirely true.

Indeed, the size of the pelvic bone apparatus is of great importance for the possibility of natural childbirth. However, even in the case of a wide pelvis, the expectant mother may experience various pathologies.

This is also no exception to prescribe a caesarean section. Surgical delivery may be indicated in case of a capacious and deep structure of the pelvic apparatus. The choice of method of delivery is determined by an obstetrician-gynecologist who monitors the course of pregnancy.

Symmetry- this is a very important parameter that the doctor must record. There is a certain medical algorithm for this. The doctor must measure the dimensions on both halves of the body. If the obtained size values on the left side are larger than those on the right side by 1 cm or more, then in this case the doctor records the presence of asymmetry.

It is important to evaluate the measured lateral dimensions as well. To do this, the doctor will measure the distance between the edge of the anterosuperior and posterosuperior bones. These clinical parameters are determined on both the left and right sides. The normal values for this indicator are 14 cm.

If the obtained values are significantly less than 12.5 cm or differ markedly from each other, this also indicates the presence of asymmetry in the pelvis of a pregnant woman. In this situation, the bones are displaced in the vertical plane.

Doctors also call this variant of the structure of the pelvic apparatus asymmetrical. In this situation, a caesarean section will usually be required. Natural childbirth can be dangerous for both the woman and her baby. The risk of various injuries in this case increases many times over.

How to measure yourself at home?

You can try to measure the size of your pelvis without the participation of a doctor. However, such measurements can only be indicative. Still, the type of structure of the pelvis and its main dimensions are determined by the obstetrician-gynecologist, who monitors the course of pregnancy in a particular woman.

The specialist has the necessary experience and knowledge to successfully carry out this important diagnostic procedure.

It often happens that the expectant mother wants to independently determine what kind of pelvis she has. To do this, she simply measures the circumference of the hips or the distance between the bone formations of the pelvis that are maximally distant from each other.

This measurement has nothing to do with the clinical determination of the size of the pelvic structure. A comprehensive and complete study can only be carried out with the participation of a doctor.