HbA1c in early diabetic pregnancy and pregnancy outcomes: a Danish population-based cohort study of 573 pregnancies in women with type 1 diabetes

Abstract

Objective: To assess the association between first-trimester HbA(1c) (A1C) and the risk of adverse pregnancy outcomes in type 1 diabetic pregnancies.

Research design and methods: We identified all pregnant diabetic women in a Danish county from 1985 to 2003. A1C values from first trimester were collected, and pregnancy outcome was dichotomized as good (i.e., babies surviving the 1st month of life without major congenital abnormalities) and adverse (i.e., spontaneous and therapeutic abortion, stillbirth, neonatal death, or major congenital abnormalities detected within the 1st month). The prevalence of adverse outcomes was calculated according to quintiles of A1C. We computed receiver operating characteristic and lowess curve estimates and fitted logistic regression models to calculate prevalence odds ratio while adjusting for confounding by White class and smoking status.

Results: Of 573 pregnancies, 165 (29%) terminated with adverse outcomes. The prevalence of adverse outcomes varied sixfold from 12% (95% CI 7.2-17) in the lowest to 79% (60-91) in the highest quintile of A1C exposure. From A1C levels >7%, we found an almost linear association between A1C and risk of adverse outcome, whereby a 1% increase in A1C corresponded to 5.5% (3.8-7.3) increased risk of adverse outcome.

Conclusions: Starting from a first-trimester A1C level slightly <7%, there is a dose-dependent association between A1C and the risk of adverse pregnancy outcome without indication of a plateau, below which the association no longer exits. A1C, however, seems to be of limited value in predicting outcome in the individual pregnancy.