They may obstruct the birth canal or cause malpresentation of the fetus.

Uterine myomas are the most common pelvic masses associated with dystocia. Soft tissue abnormalities in the pelvis occasionally can result in dystocia. 1 In the aforementioned uncommon pelvic abnormalities, it may be helpful to assess the pelvis further with imaging pelvimetry. Cesarean sections occur more frequently in women with a history of a pelvic fracture, especially bilateral fracture of the pubic rami, before pregnancy. In dwarfism, cesarean delivery is generally the rule because of marked fetopelvic disproportion. In poliomyelitis, now extremely rare, the pelvis may be asymmetric, but most patients can deliver vaginally.

With bilateral lameness, the pelvis is wide and short, but most women are able to deliver vaginally. The pelvis usually is not contracted in cases of unilateral lameness. Scoliosis, which involves the lower region of the spine, may produce an irregular inlet, leading to obstructed labor. Kyphosis, if it involves the lumbar area, may be associated with a typically funnel-shaped pelvis, which leads to late arrest of labor. Other abnormalities also may affect the bony pelvis. Of the four types of pelves, gynecoid, android, anthropoid, and platypelloid, the gynecoid pelvis is most optimal for normal delivery. It is rare to find outlet contraction without midplane contraction. The transverse diameter, the distance between the inner edges of the ischial tuberosities, measures approximately 10 cm. The anteroposterior diameter, from the inferior edge of the pubic symphysis to the tip of the sacrum, usually measures approximately 11.5 cm. The apex of the posterior triangle is the tip of the sacrum, and the sides are the sacral sciatic ligaments and ischial tuberosities. The anterior triangle is formed by the pubic arch. The pelvic outlet is composed of two triangular areas that share the same base but are not in the same plane. Midpelvic contraction is more common than inlet contraction. When the diameter is less than 9 cm, the midpelvis is considered definitely contracted. Midpelvic contraction should be suspected whenever the interspinous diameter is less than 10 cm. The anteroposterior diameter of the midpelvis, which runs from the inferior aspect of the pubic symphysis to the sacral hollow at the level of the ischial spines, averages 11.5 cm or more. The distance between the ischial spines is usually the smallest diameter of the pelvis, typically measuring 10 cm or more.

The lateral boundary is the pelvic sidewalls and ischial spines. The midpelvis is bounded anteriorly by the posterior aspect of the symphysis and pubis and posteriorly by the sacrum at the level of S3 or S4. When both diameters are contracted, the incidence of dystocia is much greater than when only one diameter is contracted. The inlet usually is considered to be contracted if the obstetric conjugate is less than 10 cm or the greatest transverse diameter is less than 12 cm. The anteroposterior diameter (obstetric conjugate) is the shortest distance between the sacral promontory and the pubic symphysis. The posterior boundary is composed of the sacrum at the level of the iliopectineal lines. The pelvic inlet is bounded laterally by the iliopectineal lines, which can be traced anteriorly along the pectineal eminence and pubic crest to the symphysis.

The anterior wall at the pubic symphysis measures approximately 5 cm, and the posterior wall measures approximately 10 cm. The “true” pelvis includes the inlet, the midpelvis, and the outlet. During labor, the fetus assumes positions and attitudes that are determined in part by the configuration of the mother’s pelvis.

Precipitate labour treatment