The Effect of Pelvic Size on Cesarean Delivery Rates: Using Adolescent Maternal Age as an Unbiased Proxy for Pelvic Size

OBJECTIVES: Dystocia, the presence of abnormal labor, is the most common indication for cesarean delivery. Risk factors for dystocia include abnormalities of expulsatile forces during labor, fetal factors, and maternal pelvic size abnormalities. The objective of our study was to evaluate the effect of pelvic size on the risk of cesarean delivery rates using adolescent maternal age as an unbiased determinant of pelvic size. METHODS: We conducted a population-based cohort study using the Center for Disease Control and Prevention's Linked Birth-Infant Death and Fetal Death data on all births in the US between 1995 and 2004 for women aged 12 to 20. We excluded all births of gestational age under 24 weeks and those with reported congenital malformations or chromosomal abnormalities. Maternal age and mode of delivery information was obtained from the birth records. RESULTS: There were 6,188,704 births in our cohort of which 1,863 were to women aged 12; 12,903 to women aged 13; 68,890 to women aged 14, and the remainder to women aged 15 and above. Cesarean delivery rates were highest amongst women aged 12 at 19.59 % and declined to 13.92% amongst 15 year-olds, and 14.84 % amongst 20 year olds. This effect was more pronounced when the analysis was restricted to macrosomic fetuses (P<0.005). CONCLUSION: Cesarean delivery rates increase the younger the maternal age is suggesting that pelvic factors can play an important role in dystocia.