Risk factors for fetal macrosomia: the importance of a positive oral glucose challenge test.

OBJECTIVE: The aim of this study was to investigate whether minor abnormalities of glucose metabolism without gestational diabetes are a risk factor for fetal overgrowth.

DESIGN: A sample of 1883 unselected white mother-infant pairs were screened for gestational diabetes using a 50 g 1-h oral glucose challenge test (GCT) in two periods of pregnancy: early (16-20 weeks) and late (26-30 weeks).

METHODS: The effects of risk factors (glucose metabolism, previous history of mothers, obesity, multiparity and age of mothers) were estimated using a multinomial logit model.

RESULTS: The level of risk was related to gestational age at the appearance of an abnormal GCT. Patients with an abnormal GCT in the early and late periods of pregnancy (Group 1) had a risk of delivering a large for gestational age (LGA) infant seven times higher than the control group (normal GCT in both periods), and patients with a normal GCT in the early period and an abnormal GCT in the late period (Group 2) showed a risk three times higher than the control group. Among the historical risk factors for LGA infants, such as maternal obesity, multiparity, previous gestational diabetes and previous delivery of an infant weighing 4000 g or more, only the latter was associated with fetal overgrowth with a risk level 4.7 higher than the control group. Group 1 patients had a significantly higher incidence of pregnancy-induced hypertension and preterm birth. There were no differences in the frequency of 5-min Apgar score < 7 and metabolic complications among the infants of all groups. We found a significantly higher rate of shoulder dystocia in Group 1 infants than in infants in the other groups.

CONCLUSIONS: Our results suggest that a positive GCT at 26-30 weeks is the most important risk factor for fetal overgrowth. This result was strongly enforced in patients who had also shown a positive early GCT at 16-20 weeks.