Chapter 25. Contracted pelvis

ICD-10 code

• O33 Maternal care for known or suspected disproportion.

- O33.0 Maternal care for disproportion due to deformity of maternal pelvic bones.

- O33.1 Maternal care for disproportion due to generally contracted pelvis.

- O33.2 Maternal care for disproportion due to inlet contraction of pelvis.

- O33.3 Maternal care for disproportion due to outlet contraction of pelvis.

- O33.4 Maternal care for disproportion of mixed maternal and fetal origin.

• O65 Obstructed labor due to maternal pelvic abnormality.

25.1. GENERAL INFORMATION

25.1.1. Epidemiology

Up till now, management of labor in presence of pelvic abnormalities presents the greatest difficulty in obstetrics. Contracted pelvis is one of the causes of perinatal morbidity and mortality, maternal injury.

The number of women with prominently contracted pelvis is on the decline; however, the average birth weight and the rate of fetal macrosomia are on the rise.

Contracted pelvis is not always an obstacle in labor. Labor complications are often related to a disproportionally large fetal head when the pelvis becomes functionally contracted.

That is why we distinguish:

• (anatomically) contracted pelvis;

• functionally contracted pelvis (cephalopelvic disproportion).

Contracted pelvis is seen in 1-7% of pregnant women; it occurs in 3% of all labors; its incidence rate shows no tendency for declining. Cephalopelvic disproportion is diagnosed at a rate of 1.3-1.7%.

25.1.2. Definition

Abroad, the inlet plane is considered contracted if the conjugate diameter is under 10 cm (the diagonal conjugate under 11.5 cm) and/or the transverse diameter of the inlet plane is under 12 cm. The true pelvis cavity is considered contracted if the total of interspinous (transverse diameter of the narrow pelvic portion) and anteroposterior diameter traced from its middle to the junction of IV and V sacral vertebrae is under 13.5 cm (15.5 cm normally). The outlet plane is assessed by the transverse diameter; it is considered contracted if the diameter is equal or less than 8 cm. A contracted pelvic outlet not related to narrowing of any other pelvic planes is noted extremely seldom.