Narrow pelvis

At present, in obstetrics it is advisable to use a classification that allows taking into account such anatomical structures of the female pelvis as the shape of the entrance and the wide part of the cavity, the size of the pelvic diameters, the shape and size of the anterior and posterior segments of the pelvis, the degree of curvature and slope of the sacrum, the shape and size of the pubic arch, etc.

In 1865, A. Ya. Krassovsky published the "Course of Practical Obstetrics", which included a description of abnormalities of the female pelvis. For the third edition of the manual (1885), A. Ya. Krassovsky rewrote the chapter on narrow pelvises. This work presents an unrivaled description of both the most typical and the rarest forms of narrow pelvises. G. G. Genter points out that "giving an exact definition of a narrow pelvis is not as easy as it seems at first glance." In most cases, narrow pelvises are those in which one of the dimensions is reduced by 1.5-2 cm compared to the average or normal dimensions. M. S. Malinovsky distinguishes:

1. anatomically narrow pelvis
2. functionally narrow pelvis.

The term "narrow pelvis" remains the main one, it is given one or another clarification depending on the clinical course of labor. The discrepancy may depend not only on the pelvis, but also on the size of the head, its ability to be configured and inserted.

In the 20th century, a number of obstetricians (Martin, Skrobansky K.K.) suggested using the term "narrow pelvis" only in relation to those pelvises that showed some signs of discrepancy between the head and the pelvis during labor; pelvises of reduced dimensions, regardless of whether they showed some signs of discrepancy during labor or not, were suggested to be designated as "narrowed" pelvises. Thus, the concept of a narrow pelvis was given a purely clinical meaning. The term "clinically narrow pelvis" began to be used in relation to pelvises of normal external dimensions, in which labor was complicated by some signs of discrepancy between the head and the pelvis.

Rational management of labor with a narrow pelvis still belongs to the most difficult sections of practical obstetrics, since a narrow pelvis is one of the causes of maternal and child trauma, as well as a cause of maternal and perinatal mortality. There is also no unified classification of a narrow pelvis. The classification below identifies four main "pure" pelvic shapes:

• gynecoid;
• android;
• anthropoid;
• platypeloid;
• "mixed" forms.

Given this classification, it is necessary to emphasize that the plane passing through the largest transverse diameter of the pelvis and the posterior edge of the ischial spines divides the pelvis into anterior and posterior segments. Mixed pelvic shapes are formed from the combination of the posterior segment of one shape with the anterior segment of another.

When determining the shape of the pelvis, the following is taken into account:

• login form;
• cavity shape;
• the size of the transverse and direct diameters;
• position of the pelvic walls;
• the shape and size of the anterior and posterior segments of the pelvis;
• the size and shape of the greater sciatic notch;
• the degree of curvature and slope of the sacrum and the shape of the pubic arch.

The pelvic cavity can be compared to an obliquely truncated cylinder.

In front, this cylinder is 4 cm high (the height of the pubis), and in the back - 10 cm (the height of the sacrum). On the sides, the height is 8 cm.

Anatomical characteristics of the main forms of the female pelvis.

Gynecoid ointment.The shape of the entrance is round or transversely oval; the anterior and posterior segments of the pelvis are well rounded, the sciatic notch is large and medium-sized, the lateral walls of the pelvis are straight, the interspinous and intertuberous diameters are wide, the slope and curvature of the sacrum are average, and the pubic arch is wide.

Android pelvis. The shape of the entrance is close to triangular, the retropubic angle is narrow, as is the anterior segment; flat and wide posterior segment, the greater sciatic notch is narrow, converging pelvic walls, short interspinous and bituberous diameters, anterior slope and lesser curvature of the sacrum, narrow pubic arch.

Anthropoid mazthe shape of the entrance is longitudinal-oval, long narrow segments of the pelvis, straight diameters of the pelvis are elongated, transverse diameters are shortened, the walls of the pelvis are straight, the slope and curvature of the sacrum are average, the large sciatic notch is of medium size, the pubic arch is somewhat narrowed.

Platypeloid maz: transverse-oval entrance shape, wide well-rounded retropubic angle, wide flat posterior segment, large sciatic notch narrow, straight pelvic walls, long transverse and shortened straight diameters of the pelvis, average slope and curvature of the sacrum.

In addition to dividing the female pelvis by shape, it is also divided by size into small, medium, and large.

The pelvis is small. Transverse diameters: the largest transverse diameter of the entrance is 11.5-12.5 cm, interspinous - 10 cm, bituberous - 9.5 cm.

Straight diameters: entrance - 10.5-11 cm, wide part - 12-12.5 cm, narrow part - 11 cm.

The pelvis is of medium size. Transverse diameters: the largest transverse diameter of the entrance is 12.5-14 cm, interspinous - 10-11 cm, bituberous - 9.5-10 cm.

Straight diameters: entrance - 11-11.5 cm, wide part - 12.5-13 cm, narrow part - 11-11.5 cm.

Large pelvis. Transverse diameters: the largest transverse diameter of the entrance is 14 cm or more, interspinous - 11-11.5 cm, bituberous - 10 cm or more.

Straight diameters: entrance - 11.5 cm or more, wide part - 13 cm or more, narrow part - 11.5 cm or more.

Of greatest interest is the management of labor in women in labor with a small pelvis - anatomically narrow. However, a narrow pelvis is currently rare; more often, erased forms of a narrow pelvis are observed. Particularly important is the assessment of the pelvis depending on its shape and size and the weight of the fetus. It has been established that the shape of the pelvis affects the mechanism of labor, and knowing the shape of the pelvis, it is possible to predict the mechanism and outcome of labor with a greater or lesser degree of probability. Whether certain signs of discrepancy between the pelvis and the head of the fetus will appear is impossible to predict in the vast majority of cases; in most cases, the final diagnosis is established during labor.

Classification by A. Ya. Krassovsky (1885)

A. Large basins.

B. Narrow pelvises.

1. Evenly tapered pelvises:
   1. generally uniformly narrowed pelvis;
   2. dwarf pelvis;
   3. baby basin.
2. Unevenly narrowed pelvises:
   1. Flat basins:
      1. simple flat pelvis;
      2. rachitic flat pelvis;
      3. flat luxation pelvis with bilateral hip dislocation;
      4. generally narrowed flat pelvis.
   2. Oblique pelvises:
      1. ankylotic oblique pelvis;
      2. coxalgic oblique pelvis;
      3. scoliosorachic oblique pelvis;
      4. kyphoscoliosarchitic oblique pelvis;
      5. pelvises with unilateral hip dislocation.
   3. Transversely contracted pelvises:
      1. ankylotic transversely narrowed pelvis;
      2. kyphotic transversely narrowed pelvis;
      3. spondylolisthetic transverse pelvis;
      4. funnel-shaped transversely narrowed pelvis.
   4. Collapsed basins:
      1. osteomalacic collapsed pelvis;
      2. rachitic collapsed pelvis.
   5. Split or open at the front pelvis.
   6. Spinous pelvises.
   7. Pelvises with neoplasm.
   8. The basins are closed.

In this classification, A. Ya. Krassovsky included both common and rare forms of narrow pelvises.

To diagnose a narrow pelvis, a woman must undergo a comprehensive examination. For example, with an anthropoid pelvis with elongated straight and shortened transverse diameters, the head is inserted by a sagittal suture in the straight or one of the oblique diameters of the pelvis, i.e. the largest diameter of the head is established in the largest diameter of the pelvis. The biparietal diameter of the head, as its narrowest dimension, passes through the narrowest diameter of the pelvis in any plane. The size of the pelvis has less effect on the mechanism of labor than its shape. In women with small pelvises, spontaneous labor is observed in cases where there is no disproportion between the size of the fetal head and the size of the pelvis. With large pelvises and a large fetus, spontaneous labor may be impossible due to a disproportion between the size of the mother's pelvis and the size of the fetal head. According to the research data, the following pelvic shapes were identified using the method of studying direct and lateral radiographs: gynecoid - in 49.9% of women, android-gynecoid - in 18.9%, flat rachitic - in 11.7%, anthropoid - in 10.6%, platypeloid - in 0.6%. In addition to the above-mentioned shapes, the authors identified a new pelvic shape in 8.3% of women, which is characterized by a shortening of the straight diameter of the wide part of the cavity due to the straightening of the curvature of the sacrum and its flattening. Due to the flattening of the sacrum, in some cases the straight diameter of the entrance may be larger than the straight diameter of the wide part of the cavity. With this pelvic structure, the capacity of the entrance will be larger than the capacity of the wide part of the cavity, and the advancement of the head along the birth canal may encounter an obstacle in the wide part of the pelvic cavity. In addition, a small pelvis was identified in 39.6% of women, an average pelvis in 53.62%, and a large pelvis in 6.78%.

In the gynecoid form, a medium-sized pelvis predominates - 81.4%, and a small pelvis in this form is observed in 13.92%. In the form of the pelvis with a shortened direct diameter of the wide part of the cavity, a small pelvis was found in 80.4%, and in a flat pelvis - in all 100% of cases. In the flat-rachitic and android-gynecoid forms, a small pelvis was detected in half of the cases.

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