Objective: Gestational diabetes is a risk factor for large-for-gestational-age (LGA) newborns, but many LGA babies are born to mothers with normal glucose tolerance. We aimed to clarify the association of maternal glycemia across the whole distribution with birth weight and risk of LGA births in mothers with normal glucose tolerance.
Research design and methods: We undertook a population-based gestational diabetes screening in an urban area of Hungary in 2002-2005. All singleton pregnancies of mothers >or=18 years of age, without known diabetes or gestational diabetes (World Health Organization criteria) and data on a 75-g oral glucose tolerance test at 22-30 weeks of gestation, were included (n = 3,787, 78.9% of the target population). LGA was determined as birth weight greater than the 90th percentile using national sex- and gestational age-specific charts.
Results: Mean +/- SD maternal age was 30 +/- 4 years, BMI was 22.6 +/- 4.0 kg/m(2), fasting blood glucose was 4.5 +/- 0.5 mmol/l, and postload glucose was 5.5 +/- 1.0 mmol/l. The mean birth weight was 3,450 +/- 476 g at 39.2 +/- 1.2 weeks of gestation. There was a U-shaped association of maternal fasting glucose with birth weight (P(curve) = 0.004) and risk of having an LGA baby (lowest values between 4 and 4.5 mmol/l, P(curve) = 0.0004) with little change after adjustments for clinical characteristics. The association of postload glucose with birth weight (P = 0.03) and the risk of an LGA baby (P = 0.09) was weaker and linear.
Conclusions: Both low and high fasting glucose values at 22-30 weeks of gestation are associated with increased risk of an LGA newborn. We suggest that the excess risk related to low glucose reflects the increased use of nutrients by LGA fetuses that also affects the mothers' fasting glucose.