Gestational diabetes mellitus in Plymouth, U.K.: prevalence, seasonal variation and associated factors.

Objective: To estimate the prevalence of and associated factors in gestational diabetes mellitus (GDM) and its seasonal variation.

Study Design: A clinic-based, prospective, case register study was conducted from January 1996 to December 1997. A total of 4,942 consecutive Caucasian, pregnant women aged 15-46 years,free of a history of diabetes mellitus, underwent random plasma glucose screening and a 75-g, 2-hour oral glucose tolerance test in Plymouth, U.K. The mean (SD) age of the women was 28.2 (5.5) years. Women with and without GDM were compared.

Results: The prevalence of GDM among the subjects was 1.8% (95% CI 1.4,2.2). The prevalence of GDM increased with the mother's age and random plasma glucose level and decreased with the duration of pregnancy. Using a stepwise binary logistic regression model, older age (relative prevalence [RP] 1.08 [95% CI 1.04, 1.12]) and higher random plasma glucose (RP 2.99 [95% CI 2.51, 3.551) were significant predictors of GDM. The monthly prevalence of GDM ranged from 2.9% (95% CI 1.5, 5.0) in June to 1.1% (95% CI 0.3,2.8) in November. The seasonal GDM rate ranged from 2.3% (95% CI 1.5, 3.2) in spring to 1.4% (95% CI 0.8, 2.3) in winter. The differences were not statistically significant for either the month (p = 0.82) or season (p = 0.41).

Conclusion: The prevalence (1.8%) of GDM in this representative sample of Caucasian pregnant women was lower than the 3-5% typically reported in other European and North American studies, and there was no seasonal pattern.