Clinically narrow pelvis

At present, the concept of an anatomically and clinically narrow pelvis has been clearly defined and the predominance of the latter has been revealed.

A clinically narrow pelvis means a discrepancy between the fetal head and the woman's pelvis, regardless of the size of the latter. A very important point is that incorrect interpretation of the concept of "clinically narrow pelvis" also leads to the fact that all cases of discrepancy between the pelvis and the head with normal pelvic sizes, arising as a result of various unfavorable factors (excessive size of the head, incorrect insertion, etc.), are not considered as a clinically narrow pelvis in most maternity hospitals.

Therefore, this group of obstetric pathology should include not only cases of discrepancy that ended with surgery, but also spontaneous labor, if the course of the labor act, the features of the insertion of the head and the mechanism of labor indicated a disproportion between the pelvis and the head. This, apparently, can also explain the fact that the main indication for cesarean section is an anatomically and clinically narrow pelvis in every 3-5th woman, and according to foreign authors - in 40-50% of primary cesarean sections.

There is no consensus on the definition of the concept of an anatomically narrow pelvis. Thus, some obstetricians include all pelvises whose bone skeleton has an abnormal development and shape. Other doctors are guided by a decrease in all external dimensions of the pelvis by 1.5-2 cm. Most obstetricians consider a decrease in one of the main dimensions - the external conjugate, taking as the initial limit a size equal to 19; 18; 17.5 and 17 cm.

However, the most correct and accurate is the determination of the true conjugate obtained by subtracting 1.5 cm for a generally uniformly narrowed pelvis and 2 cm for a flat pelvis from the value of the diagonal conjugate measured during an internal examination. Often, when comparing the values of the external and internal (true) conjugates obtained in the same woman, a noticeable difference is found, depending on the thickness of the pelvic bones; a well-known idea of this is given by the Soloviev index mentioned above.

This is important because the frequency of narrow pelvises changes depending on the initial value of the external conjugate. Thus, if the external conjugate is taken to be 19 cm or less, the percentage of narrow pelvises will be high, at 18 cm - 10-15%, at 17.5 cm - 5-10%. On average, the frequency of narrow pelvises fluctuates from 10 to 15%, while narrow pelvises that cause serious violations of the act of childbirth are observed only in 3-5%.

The assessment of the degree of pelvic narrowing also varies. Some obstetricians are guided by three, others - by four degrees of narrowing, taking as a basis the normal value of the true conjugate, equal to 11 cm. Perhaps it is more appropriate to focus on the value of the diagonal conjugate, since each time it is necessary to subtract 1.5-2 cm from it to obtain the size of the true conjugate.

The introduction of X-ray pelvimetry, ultrasound methods of examination, and the use of full scanning of the entire pelvis using computerized axial tomography into obstetric practice have made it possible to identify forms of narrow pelvis that are little known to a wide range of obstetricians. These include the assimilatory pelvis or "long pelvis" mentioned by us, as well as a pelvis with shortened direct dimensions of the cavity.

According to modern data, the frequency of anatomically narrow pelvis fluctuates between 2 and 4%. At the same time, the structure of various forms of narrow pelvis has changed: the most common (up to 45%) is a pelvis with narrowing of transverse dimensions. The second place in frequency (22%) is occupied by a pelvis with a decrease in the direct size of the wide part of the cavity and flattening of the sacrum.

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