Anthropometric predictors of cephalopelvic disproportion

Background: The discrepancy between the sizes of the maternal pelvis and fetus is associated with high operative delivery rates, as well as obstetric and neonatal morbidity and mortality. The use of classical pelvimetry to predict cephalopelvic disproportion is currently considered insufficient. Evidence suggests that in the formation of a clinically narrow pelvis, the ratio of the head circumference to the maternal height plays a major role rather than the body weight of the fetus. Therefore, studying the anthropometric data of both the mother and fetus during full-term pregnancies in Russia is essential for identifying the risk groups for clinically narrow pelvises.

Objective: To investigate the prognostic significance of anthropometric data of women and fetuses at full term concerning the risk of a clinically narrow pelvis.

Materials and methods: This retrospective cohort study analyzed 12,034 delivery case records, which were divided into two groups. The study group (n=183) comprised women who underwent cesarean delivery due to a narrow pelvis, while the control group (n=915) included women who underwent vaginal delivery.

Results: The highest frequency of a clinically narrow pelvis and operative abdominal delivery was observed with a head circumference >342.15 mm and fetal body weight >3670 g. The median ratio of fetal head circumference measured by ultrasound to maternal height in the vaginal delivery group was lower, at 2.0 (1.94; 2.05), compared to 2.08 (2.02; 2.13) in the clinically narrow pelvis group (p<0.001).

Conclusion: The ratio of fetal head circumference to maternal height was lower in vaginal deliveries, measuring 2.0 versus 2.08 for the clinically narrow pelvis group. A fetal body weight of 3670 g and head circumference above 342.15 mm, as measured by ultrasound one week before the onset of labor, likely represent the threshold beyond which the probability of cephalopelvic disproportion significantly increases.