Excess gestational weight gain: modifying fetal macrosomia risk associated with maternal glucose.

OBJECTIVE: To estimate how maternal weight gain and maternal glucose relate to fetal macrosomia risk (greater than 4,000 g) among a population universally screened for gestational diabetes mellitus (GDM).

METHODS: Between 1995 and 2003, 41,540 pregnant women in two regions (Northwest/Hawaii) of a large U.S. health plan had GDM screening using the 50-g glucose challenge test; 6,397 also underwent a 3-hour, 100-g oral glucose tolerance test. We assessed the relationship between level of maternal glucose with glucose screening and fetal macrosomia risk after adjustment for potential confounders, including maternal age, parity, and ethnicity and sex of the newborn. We stratified by maternal weight gain (40 lb or fewer compared with more than 40 lb) because excessive maternal weight gain modified results.

RESULTS: Among women with both normal and abnormal GDM screenings, increasing level of maternal glucose was linearly related to macrosomia risk (P<.001 for trend in all groups). Women with excessive weight gain (more than 40 lb) had nearly double the risk of fetal macrosomia for each level of maternal glucose compared with those with gestational weight gain of 40 lb or fewer. For example, among women with normal post-glucose challenge test glucose levels (less than 95 mg/dL) and excessive weight gain, 16.5% had macrosomic newborns compared with 9.3% of women who gained 40 lb or fewer. Moreover, nearly one third of women (29.3%) with GDM who gained more than 40 lb had a macrosomic newborn compared with only 13.5% of women with GDM who gained 40 lb or fewer during pregnancy (P=.018).

CONCLUSION: Excessive pregnancy weight gain nearly doubles the risk of fetal macrosomia with each increasing level of maternal glucose, even among women with GDM.

LEVEL OF EVIDENCE: II.