Clinically narrow pelvis

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

A clinically narrow pelvis means a mismatch between the head of the fetus and the pelvis of a woman, regardless of the size of the latter. A very important point is that the misinterpretation of the concept of "clinically narrow pelvis" also leads to the fact that all cases of incompatibility between the pelvis and the head at normal pelvic dimensions, resulting from various adverse factors (excessive head size, incorrect insertion of it, etc.), in most maternity hospitals are not considered as a clinically narrow pelvis.

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

In the definition of the concept of an anatomically narrow pelvis there is no consensus. Thus, some obstetricians refer to them all the pelvic bone skeleton which has an irregular development and shape. Other doctors are guided by a reduction in all external dimensions of the pelvis by 1.5-2 cm. Most obstetricians consider a decrease in one of the main dimensions - the outer conjugate, taking the size equal to 19 for the initial border; 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 with a generally uniformly compressed pelvis and 2 cm at a flat of the diagonal conjugate measured by internal investigation. Often, when comparing the values of the external and internal (true) conjugates obtained from the same woman, a significant difference is found, depending on the thickness of the pelvic bones; A well-known idea of this is given by the Solov'ev index mentioned above.

This is important, because depending on the acceptance of the initial value of the outer conjugate, the frequency of the narrow basins also changes. So, if you take an external conjugate equal to 19 cm or less, the percentage of narrow cans will be high, at 18 cm - 10-15%, at 17.5 cm - 5-10%. On average, the frequency of narrow cans varies from 10 to 15%, while the narrow pelvis causing severe disturbances of the birth act is observed only in 3-5%.

The evaluation and the degree of narrowing of the pelvis are different. Some obstetricians are guided by three, others by four degrees of constriction, taking as a basis the normal value of the true conjugate equal to 11 cm. It may be more expedient to orientate at once to the value of the diagonal conjugate, since all the same it must be subtracted 1.5-2 cm each time obtaining the size of the true conjugate.

The introduction of X-ray and pellvimetry, ultrasound methods in obstetric practice, and the use of a full scan of the entire pelvis with computerized axial tomography made it possible to identify forms of the narrow pelvis that are not widely known to a wide range of obstetricians. These include the assimilation pelvis or "long pelvis" mentioned by us, as well as a pelvis with a shortening of the direct dimensions of the cavity.

According to modern data, the incidence of the anatomically narrow pelvis varies from 2 to 4%. This changed the structure of various forms of the narrow pelvis: most often (up to 45%) there is a pelvis with a narrowing of the transverse dimensions. The second place in frequency (22%) is occupied by the pelvis with a decrease in the direct size of the wide part of the cavity and the flattening of the sacrum.

[1], [2], [3], [4], [5], [6]