Smoking Affects The Oral Glucose Tolerance Test Profile And The Relationship Between Glucose And Hba(1c) In Gestational Diabetes Mellitus

AimsCurrent smokers in the general population have a lower 2 h plasma glucose after an oral glucose tolerance test (OGTT) and a higher HbA(1c) than non-smokers, but the relationships between OGTT/HbA(1c) and smoking status have not been addressed in pregnancy. We analysed glycaemic measurements in women with gestational diabetes mellitus in relation to smoking status.MethodsWe performed a review of the prospectively collected database of the diabetes and pregnancy clinic. We included women with gestational diabetes mellitus and a singleton pregnancy who delivered between 1986 and 2006. Bivariate and multivariate analyses were used to evaluate patient characteristics in relation to smoking status.ResultsA total of 2361 women met the inclusion criteria: 556 (23.5%) were active smokers, 266 (11.3%) quit during pregnancy and 1539 (65.2%) were non-smokers. Most baseline characteristics were similar across groups. Diagnostic OGTT was performed at a gestational age of [median (25th, 75(th) centiles)] 29 weeks (26, 33). Women who smoked at the beginning of pregnancy had a higher 1-h plasma glucose than non-smokers [11.8 (11, 12.7), 11.6 (11, 12.6) and 11.5 (10.8, 12.5) mmol/l, for active smokers, those who quit during pregnancy and non-smokers, respectively, P < 0.001] and a lower 3-h plasma glucose [7.3 (5.9, 8.4), 7.6 (6.4, 8.7) and 8.0 (6.8, 9.0) mmol/l, respectively, P < 0.001]. HbA(1c) was higher in women who smoked at the beginning of pregnancy. Multiple regression analysis confirmed the independent association of smoking status with HbA(1c) and OGTT plasma glucose.ConclusionsIn women with gestational diabetes mellitus who smoke at the beginning of pregnancy, the shape of the OGTT is consistent with accelerated glucose absorption, and HbA(1c) is higher than expected for glycaemic values.