Maternal obesity and induction of labor.

OBJECTIVE: To review induction of labor analyzed by body mass index (BMI) category in primigravidas and multigravidas.

DESIGN: Prospective observational study.

POPULATION: Women enrolled after sonographic confirmation of singleton pregnancy in the first trimester.

SETTING: Large university teaching hospital.

METHODS: Maternal height and weight were measured accurately before BMI calculation. Clinical details were recorded after review of individual obstetric records.

MAIN OUTCOME MEASURES: Emergency cesarean section and obstetric interventions.

RESULTS: Of 2000 women enrolled, 50.4% (n = 1008) were primigravidas and 17.3% (n = 346) were obese. The induction rate was 25.6% and the overall cesarean section rate 22.0%. Primigravidas were more likely to have labor induced than multigravidas (38.1% vs. 23.4%, p < 0.001). Compared with women with a normal BMI, obese primigravidas but not obese multigravidas were more likely to have labor induced. In primigravidas who had labor induced, the cesarean section rate was 20.6% (91/442) compared with 8.3% (17/206) in multigravidas who had labor induced (p < 0.001). In obese primigravidas, induction of labor was also more likely to be associated with other interventions such as epidural analgesia, fetal blood sampling and emergency cesarean section. In contrast, induction of labor in obese multigravidas was not only less common but also not associated with an increase in other interventions compared with multigravidas with a normal BMI.

CONCLUSIONS: Due to the short-term and long-term implications of an unsuccessful induction in an obese primigravida, we recommend that induction of labor should only be undertaken for strict obstetric indications after careful consideration by an experienced clinician.