Associations of gestational weight loss with birth-related outcome: a retrospective cohort study.

OBJECTIVE: Although the prevention of gestational weight loss (GWL) has become a priority for clinicians in the past few decades, recent work has suggested that GWL may be beneficial for obese mothers. We aimed to identify the potential beneficial or adverse associations of GWL with pregnancy outcome stratified by maternal body mass index (BMI) category.

DESIGN: Retrospective cohort study.

SETTING AND POPULATION: Data on 709 575 singleton deliveries in Bavarian obstetric units from 2000-2007 were extracted from a standard dataset for which data are regularly collected for the national benchmarking of obstetric units.

METHODS: We calculated the odds ratios (ORs) for adverse pregnancy outcome by GWL (explanatory variable) compared with nonexcessive weight gain with adjustment for confounders and stratification by BMI category (underweight, BMI < 18.5 kg/m²; normal weight, BMI = 18.5-24.9 kg/m²; overweight, BMI = 25-29.9 kg/m²; obese class I, BMI = 30-34.9 kg/m²; obese class II, BMI = 35-39.9 kg/m²; obese class III, BMI ≥ 40 kg/m²).

MAIN OUTCOME MEASURES: Pre-eclampsia, nonelective caesarean section, preterm delivery, small or large for gestational age (SGA/LGA) birth and perinatal mortality.

RESULTS: GWL was associated with a decreased risk of pregnancy complications, such as pre-eclampsia and nonelective caesarean section, in overweight and obese women [e.g. OR = 0.65 (95% confidence interval: 0.51, 0.83) for nonelective caesarean section in obese class I women]. The risks of preterm delivery and SGA births, by contrast, were significantly higher in overweight and obese class I/II mothers [e.g. OR = 1.68 (95% confidence interval: 1.37, 2.06) for SGA in obese class I women]. In obese class III women, no significantly increased risks of poor outcomes for infants were observed.

CONCLUSIONS: The association of GWL with a decreased risk of pregnancy complications appears to be outweighed by increased risks of prematurity and SGA in all but obese class III mothers.