Pre-Pregnancy Physical Fitness, Body Mass Index and Gestational Weight Gain as Risk Factors for Cesarean Delivery: A Study of Active Duty Women.

Abstract

The World Health Organization considers the optimal rate of delivery by Cesarean among healthy nulliparous women to be <15%. In 2020, the rate of primary Cesarean delivery (CD) in the US among nulliparous women with singleton, vertex pregnancies was 26%. An enhanced understanding of factors associated with women undergoing CD may assist in reducing this rate. One potential factor is the level of physical fitness in women before pregnancy. Active duty (AD) soldiers provide a cohort of women who begin pregnancy while actively pursuing physical fitness. The research team sought to assess the effects of pre-pregnancy physical fitness of AD soldiers as measured by the Army Physical Fitness Test (APFT) on the incidence of CD in AD women, in addition to examining known demographic and pregnancy risk factors in this cohort. We conducted a retrospective study of healthy AD nulliparous women who delivered their singleton pregnancy of >32 weeks at a tertiary medical center between 2011 and 2016. Soldiers undergoing non-labored CD were excluded. Demographics, pre-pregnancy APFT results, antepartum and labor and delivery data were collected from the Digital Training Management System, the outpatient, and inpatient medical records respectively. Weight gain in pregnancy was assessed using the Institute of Medicine Guidelines for pregnancy. Fisher's exact tests and chi-squared tests assessed associations between categorical outcomes, and unpaired t-tests assessed differences in APFT scores between women who underwent CD vs. vaginal delivery. Multivariable logistic regression analysis was used to assess for independent risk factors among all collected variables. The protocol was approved by the Regional Health Command-Pacific Institutional Review Board. Five-hundred-and-twenty-three women delivering singleton pregnancies between 2011 and 2016 were reviewed for this study. Three-hundred ninety women met inclusion criteria: 316 in the vaginal delivery cohort, and 74 in the CD cohort, with a CD rate of 19%. Twenty non-labored CDs were excluded. Neither total APFT performance nor performance on the individual push-up, sit-up or run events in the 15 months prior to pregnancy was associated with mode of delivery. Excessive gestational weight gain (EWG) and neonatal birth weight were the only two factors independently associated with an increased rate of cesarean delivery. Women who had excessive gestational weight gain, were twice as likely to undergo CD as those who had adequate or insufficient weight gain (24% vs. 12%, p = 0.004). Soldiers delivering a neonate ≥4,000 g were 2.8 times as likely to undergo CD as those delivering a neonate <4,000 g (47% vs. 17%, p < 0.001). Age, race, and rank, a surrogate marker for socioeconomic status, were not associated with mode of delivery. Pre-pregnancy fitness levels as measured by the APFT among healthy physically active nulliparous AD women showed no association with the incidence of labored CD. EWG is one modifiable factor which potentially increases the risk for CD in this cohort and has been documented as a risk factor in a recent metanalysis (RR-1.3). Counseling on appropriate weight gain in pregnancy may be the most effective way to reduce the rate of CD among this population of healthy and physically active women.