Obstructed Labor, Evolution, and Health Disparities

Abstract

The female pelvis is often evolutionarily described as a compromise to accommodate the birthing process and bipedalism. This compromise puts a mother and baby at risk of fetopelvic disproportion, the mismatch between the size of the fetus and that of the mother's pelvis, impacting the ease with which the vaginal birthing process occurs. Obstructed labor, commonly caused by fetopelvic disproportion, is a leading cause of maternal mortality and morbidity and has serious medical sequelae for the fetus. In this review, this evolutionary aspect of fetopelvic disproportion is reconsidered within a broader sociocultural and environmental approach related to a change of paradigm from a more reductionist Neo-Darwinist to a more encompassing Extended Evolutionary Synthesis view. The review explores a more comprehensive understanding of several factors related to fetopelvic disproportion, including socioeconomic factors and ethnic disparities among individuals that might lead to a higher likelihood of obstructed labor and maternal and fetal morbidity and mortality.

Keywords: childbirth; fetopelvic disproportion; obstetric dilemma; obstetrical pelvis; obstructed labor.

Figure 1

The human pelvis is organized and measured as follows. Three anteroposterior (A, B, C) and mediolateral planes create the birth canal (D, E, F): the inlet, the midplane, and the outlet, respectively (figure modified from Betti, 2017 [15]).

Figure 2

A normal-sized pelvis (left) compared to a contracted pelvis (right) (figure modified from Loudon, 1997 [34]).

Figure 3

Association between incidence of intrapartum cesareans per 1000 deliveries and maternal height among women in Ouagadougou, Burkina Faso (figure modified from Wells, 2017, with data from Sokal et al. 1991 [36]).

Figure 4

The four parent pelvis shapes coined by Caldwell and Moloy in 1938 (figure modified from Betti, 2021 [15].