The conjugate is true, external, diagonal. Sizes of a woman's small pelvis

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 drawing up a pregnant card when a woman first visits a gynecologist. Based on the size of the pelvis, you can plan the management of labor: by natural means or by the surgical method (cesarean section). Timely chosen tactics avoids many complications that pose a threat to the life of a woman and her baby. Properly planned birth is a guarantee that the birth of a child will be easy and safe.

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 is a small pelvis?

The pelvis as an anatomical formation is represented by two pelvic bones and the distal spine (sacrum and tailbone). In obstetrics, only that part of it, which is called the pelvis, is important. This is the space bounded by the lower parts of the pelvic bones, the sacrum and tailbone. 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.

Entrance to the pelvis

1. The size is straight. This indicator has other names - obstetric conjugate and true conjugate. It is equal to 110 mm.
2. The size is transverse. It is equal to 130-135 mm.
3. The dimensions are oblique. Equal to 120-125 mm.
4. Diagonal conjugate. It is equal to 130 mm.

Parameters of the wide part of the pelvis

1. The size is straight. It is equal to 125 mm.
2. The size is transverse. It is equal to 125 mm.

Parameters of the narrow part of the pelvis

1. The size is straight. It is equal to 110-115 mm.
2. The size is transverse. It is equal to 105 mm.
   

Pelvic exit parameters

1. The size is straight. During childbirth, it can increase, as the fetal head advancing along the birth canal bends the tailbone posteriorly. It is 95-115 mm.
2. The size is transverse. It is equal to 110 mm.

Pregnant pelvis measurement

The above indicators are anatomical, that is, they can be determined directly by the bones of the pelvis. On a living person it is not possible to measure them. Therefore, in obstetric practice, the following parameters are most important:

1. The distance between the iliac spines located at the front edge of the ridge.
2. The distance between the points of the crests of the iliac bones, distant from each other to the maximum distance.
3. The distance between the protrusions of the femurs in the area of ​​transition of their upper part to the neck.
4. External conjugate (distance from the pubic symphysis to the lumbosacral depression).

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 instrument (tazomer), which, by the way, can also be used to measure the head of a born 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 estimated by the bony protrusions, and they do not move anywhere when losing weight or, on the contrary, gaining weight. The size of the pelvis remains unchanged after a woman reaches the age when bone growth stops.

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

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

What is a narrow basin?

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 mentioned when at least one of the parameters is less than the normal size of the pelvis. The degree of narrowing is distinguished when the conjugate is true less than normal:

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

The last two degrees indicate the need for surgical intervention. The true conjugate of the 1-2st degree allows the possibility of continuing the birth naturally, provided that there is no threat of a condition such 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 normal limits (that is, from the point of view of anatomy, this pelvis is not always narrow). There may be a reverse situation when the anatomically narrow pelvis is fully consistent with the configuration of the fetal head (for example, if the child is not large), and there is no question of a diagnosis of a clinically narrow pelvis in this case.

Clinically narrow pelvis

The main causes of this condition:

1. From the side of the mother: anatomically small size of the pelvis, irregular shape of the pelvis (for example, deformation after an injury).
2. From the side of the fetus: hydrocephalus, large size, postponement of pregnancy, tilting of the head when the fetus enters the small pelvis.

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

1. Relative mismatch. In this case, an independent birth is possible, however, the doctor must be ready to make a timely decision on surgical intervention.
2. Significant mismatch.
3. Absolute mismatch.

Clinically narrow pelvis

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

With relative mismatch, childbirth is naturally acceptable. However, one should keep in mind the danger of changing the situation for the worse. The doctor must accept the question of the severity of the discrepancy even during the period of contractions, in order to timely determine the further tactics. Belated diagnosis of conditions when delivery should only be performed surgically can lead to serious difficulties with the removal of the fetal head. With severe discrepancy, the latter will be driven into the pelvic cavity by a 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 cesarean section. In such cases, childbirth has to end with a fruit-destroying operation.

To summarize

Know the size of the pelvis is necessary. This is necessary in order to timely suspect pathological conditions such as anatomically and clinically narrow pelvis. Reducing the normal size can be of varying degrees of severity. In some cases, independent delivery is even possible; in other situations, it becomes necessary to perform a caesarean section.

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