Background: Rising rates of cesarean births and an increasing number of patients, especially primiparous women, requesting cesarean delivery have stimulated interest in the delivery method's impact on subsequent pregnancies. Initial studies have reported an increase in unexplained stillbirths and other adverse outcomes after a previous cesarean delivery. These adverse effects cannot be attributed to the delivery method without adjusting for many factors, in particular the indication for the initial cesarean delivery. Kennare and colleagues analyzed differences in second pregnancy outcomes between women who had a previous cesarean delivery and those who had a previous vaginal delivery.

The Study: The large retrospective study included singleton second births to women in South Australia from 1998 to 2003. Data were abstracted from a validated, comprehensive, statewide pregnancy reporting system that included sociodemographic, pregnancy, birth, and neonatal information on all live and stillbirths that had a gestational age of at least 20 weeks or that had a birth weight of at least 14.1 oz (400 g). The statistical analyses adjusted for age, indigenous status, smoking status, pregnancy interval, medical conditions (i.e., hypertension, diabetes, or asthma), obstetric complications, patient insurance status (i.e., public or private), gestational age, and obstetric history (i.e., ectopic pregnancy, miscarriage, stillbirth, or termination).

Results: More women who had a previous cesarean delivery were 30 years or older and were privately insured patients compared with those who had a previous vaginal delivery. Conversely, fewer women in the previous cesarean delivery group were smokers or had pregnancy intervals less than 15 months.

Women who delivered their first child by cesarean had a significantly increased risk of adverse outcomes in their second pregnancy, including placenta previa, antepartum hemorrhage, malpresentation, prolonged labor, and cesarean delivery; the risk of emergency cesarean delivery increased the most (see accompanying table). Rare events such as uterine rupture and placenta accreta also were significantly more common in mothers who delivered their first child by cesarean. Two maternal deaths occurred in the previous cesarean delivery group (one from hemorrhage following hysterectomy for placenta accreta and one from amniotic fluid embolism following uterine rupture). There were no maternal deaths in the vaginal delivery group. Infants whose mothers had a previous cesarean delivery had increased risk of being small for gestational age, premature, or stillborn.

Conclusion: The authors conclude that a first cesarean delivery is associated with increased risk of adverse outcomes in a subsequent pregnancy. They believe these findings have serious implications for women who elect to have their first child via cesarean delivery.