Abstract

Objective – Gestational diabetes is a risk factor for large for gestational age (LGA) newborns, but many LGA babies are born to normal glucose tolerant mothers. We aimed to clarify the association of maternal glycemia across the whole distribution with birthweight and risk of LGA births in normal glucose tolerant mothers.

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 ≥18 years of age, without known diabetes or gestational diabetes (WHO criteria) and data on 75g oral glucose tolerance test at 22-30 weeks of gestation were included (n=3787, 78.9% of the target population). LGA was determined as >90th percentile using national sex and gestational age specific charts.

Results – Mean±SD maternal age was 30±4 years, BMI 22.6±4.0 kg/m2, fasting blood glucose 4.5±0.5 mmol/L and postload glucose 5.5±1.0 mmol/L. The mean birthweight was 3450±476 grams at 39.2±1.2 weeks of gestation. There was a U-shaped association of maternal fasting glucose with birthweight (p_curve=0.004) and risk of having a LGA baby (lowest values between 4-4.5 mmol/L, p_curve=0.0004) with little change after adjustments for clinical characteristics. The association of postload glucose with birthweight (p=0.03) and the risk of LGA (p=0.09) was weaker and linear.

Conclusions – Both low and high fasting glucose at 22-30 weeks of gestation are associated with increased risk of 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.