Utilizing retrospective data, a University of Kentucky team set out to examine the relationship between previous caesarean delivery and subsequent preterm birth. Their results appear in the European Journal of Obstetrics & Gynecology and Reproductive Biology.
Although the rate of birth by cesarean (“C-section”) has increased over time worldwide, the United States in particular has experienced a dramatic increase in the rate of cesarean delivery over the last several decades. Just from 1996 to 2010, the U.S. saw a 60 percent increase in cesarean births. From 2010 to 2012 the rate plateaued at 32.8 percent; since 2013, the country has seen a slight decrease each year in the number for cesarean sections performed among all live births, with the most recent rate being 31.9 percent. Although medically necessary cesarean sections provide many benefits to mother and child, the World Health Organization recognizes that — at the population level — when cesarean rates are higher than 10 percent, there is no increase in beneficial maternal and newborn outcomes. In fact, some researchers note that in countries where cesarean rates are above 15 percent, populations experience higher maternal, infant, and neonatal mortality rates.
Poor outcomes for individual infants and mothers have also been associated with cesarean delivery. Compared to infants born vaginally, infants born by cesarean delivery are more likely to require NICU care and have greater respiratory complications, and higher odds for childhood asthma, and obesity. Women are more likely to experience placenta previa, placental abruption, uterine rupture, placenta accrete, miscarriage, ectopic pregnancy, subfertility, and stillbirth in their second pregnancy after a cesarean section first birth.
The retrospective cohort study utilized 2016 United States birth certificate data to generate the study population, which consisted of 1,076,517 women delivering a single infant (not a multiple birth) in their second live birth. Pre-term birth and previous cesarean delivery measures were also derived from US birth certificates. Covariates included: maternal age, race/ethnicity, education, marital status, payer source for delivery, pre-pregnancy body mass index, previous preterm birth, interpregnancy interval, and factors in the second pregnancy such as hypertensive disorders, diabetes, and cigarette use, trimester prenatal care began, weight gain during pregnancy, and presence of congenital anomalies. Women who had experienced a cesarean delivery of their first pregnancy were compared to those who did not.
When controlling for all covariates, women who had a cesarean delivery in their first pregnancy were found to be 14 percent more likely to have a preterm birth in their second pregnancy compared to women who had not previously experienced a previous cesarean delivery. When risk was analyzed by sub0categories of preterm birth based on gestational age, a differential association was noted, with a 10 percent increased risk of delivering before 34 weeks, a 1 percent increased risk for delivery between 34 and 36 weeks, and no increased risk for delivery after 36 weeks compared to delivery at 39 to 40 weeks.
This small, but statistically significant association between previous cesarean section and subsequent preterm birth suggests that efforts to reduce the number of index cesarean sections may contribute to reducing the overall preterm birth rate in the United States.
The lead author of the paper “Previous cesarean delivery associated with subsequent preterm birth in the United States” is Dr. Corrine M. Williams, associate professor of health, behavior & society at the University of Kentucky College of Public Health. Co-authors from the College of Public Health are research assistants Ms. Ibitola Asaolu, Ms. Lucy H. Williamson, and Ms. Alysha M. Lewis. Faculty co-authors are Dr. Niraj R. Chavan and Dr. Lauren Beaven of the UK College of Medicine, and Dr. Kristin B. Ashford of the UK College of Nursing.