Increased second trimester maternal glucose levels are related to extremely large-for-gestational-age infants in women with type 1 diabetes.

OBJECTIVE: Large-for-gestational-age (LGA) infants (birth weight > or = 90th centile) are a continuing problem in pregnancies of women with type 1 diabetes. We used the continuous glucose monitoring system (CGMS) to assess the relationship between 24-h diurnal glucose profiles in all three trimesters of pregnancy and infant birth weight.

RESEARCH DESIGN AND METHODS: Twenty-nine pregnant women with type 1 diabetes used the CGMS during each trimester of pregnancy. The glucose profiles of the women with a normal-weight infant or an LGA infant were compared.

RESULTS: Of the women with type 1 diabetes, 48% gave birth to an LGA infant. Fifty percent of these infants were already large for dates on ultrasound at < 30 weeks of gestation (early LGA), and all these infants had a birth weight > or = 97.7th centile. The diurnal glucose profiles show that the mothers of early LGA infants had elevated glucose levels for most of the day during the second trimester (P < 0.05). The median 24-h glucose level was significantly higher in women who gave birth to early LGA infants in all three trimesters of pregnancy (6.7, 8.3, and 6.5 mmol/l for the first, second, and third trimesters, respectively). Within the group of women with early LGA infants, the second trimester median glucose level was significantly higher than that in the first and third trimester (P < 0.05).

CONCLUSIONS: In women with type 1 diabetes, extreme growth of the fetus starts early in pregnancy and is likely caused by increased maternal glucose levels. Further investigation is needed to see whether early tight glycemic control will reduce the number of extreme LGA infants.