Maternal body mass index in the first trimester and risk of cesarean delivery in nulliparous women in spontaneous labor.

OBJECTIVE

To evaluate the effect of maternal body mass index (BMI) on the incidence of cesarean delivery.

STUDY

DESIGN

Prospective observational cohort study of 4341 consecutive nulliparous women with a single cephalic presentation, and spontaneous onset of labor between 37 and 42 weeks gestation at High Wycombe General Hospital, London, between January 1, 1995, and December 31, 2000.

RESULTS

The incidence of cesarean delivery rose significantly with an increase in BMI. Women in labor with a BMI > 35 had a 3.8 times greater chance of a cesarean delivery than women with a BMI < 25 (after adjustment for variables such as maternal height and age, gestational age, fetal birthweight, and use of oxytocin and epidural analgesia during labor). This was true for cesarean deliveries performed for suspected fetal distress as well as for failure to progress.

CONCLUSION

A high BMI significantly increased the risk of cesarean delivery, but the reasons are not certain.