Both elective and emergency cesarean sections in first births appear to slightly increase the risk of stillbirth and ectopic pregnancy in subsequent pregnancies, according to a new study.
Compared with women whose first birth was a spontaneous vaginal delivery, primiparous women with a primary C-section were 14% more likely to have a subsequent stillbirth and 9% more likely to have a later ectopic pregnancy, but were no more likely to have a subsequent miscarriage, reported Sinéad O’Neill of Cork University Maternity Hospital, Ireland, and her associates (PLoS Med. 2014 July 1 [doi:10.1371/journal.pmed.1001670]).
The analysis was limited by incomplete data, and the increased rate of stillbirths and/or ectopic pregnancies could be driven by underlying factors that contributed to the need for a C-section, the researchers noted.
They analyzed Danish national registry data on 832,996 primiparous women with a live birth between Jan. 1, 1982, and Dec. 31, 2010, followed until the next stillbirth, miscarriage, ectopic pregnancy, live birth, death or emigration. Miscarriage was defined as loss before 28 weeks’ gestation until April 2004, and before 22 weeks’ gestation from 2004 onward.
The fully-adjusted analysis controlled for the following:
• Maternal age, origin, and marital status.
• Previous stillbirth, miscarriage, or ectopic pregnancy.
• Birth year.
• Socioeconomic status (mother’s education and both parents’ gross income).
• Medical complications in the first live birth, including multiples, diabetes, gestational diabetes, placental abruption, placenta previa, and hypertensive disorders.
• Gestational age at birth and birth weight.
The researchers lacked data on maternal body mass index, smoking status, and fertility treatment, as well as causes of stillbirth, maternally requested C-sections, and the gestational ages of the stillbirths and miscarriages.
The increased rate of stillbirth (hazard ratio 1.14) among women with a primary C-section, compared with women with an initial spontaneous vaginal birth, translated to an absolute risk increase of 0.03% and a number needed to harm of 3,333. Emergency C-sections showed a barely higher risk (HR 1.15), but the risk with elective C-sections (HR 1.11) did not reach statistical significance (95% CI 0.91, 1.35).