First trimester coffee and tea intake and risk of gestational diabetes mellitus: a study within a national birth cohort.

Objective: Coffee and tea consumption is associated with a decreased type 2 diabetes risk in non-pregnant adults. We examined the relation between first trimester coffee and tea consumption and gestational diabetes mellitus (GDM) risk.

Design: Population-based cohort study.

Setting: Denmark 1996-2002.

Population: Non-diabetic women with singleton pregnancies in the Danish National Birth Cohort (n = 71,239).

Methods: Estimated adjusted relative risks (RR) and 95% confidence intervals (95%CI) for the association between first trimester coffee and tea or estimated total caffeine and GDM.

Main Outcome Measures: GDM ascertained from the National Hospital Discharge Register or maternal interview.

Results: Coffee or tea intake was reported in 81.2% (n = 57,882) and 1.3% (n = 912) of pregnancies were complicated by GDM. Among non-consumers, 1.5% of pregnancies were complicated by GDM. Among coffee drinkers, GDM was highest among women who drank ≥8 cups/day (1.8%) with no significant difference across intake levels (P = 0.10). Among tea drinkers, there was no difference in GDM across intake levels (1.2%; P = 0.98). After adjustment for age, socio-occupational status, parity, pre-pregnancy body mass index, smoking, and cola, there was suggestion of a protective, but non-significant association with increasing coffee (RR ≥8 versus 0 cups/day = 0.89 [95%CI 0.64-1.25]) and tea (RR ≥8 versus 0 cups/day = 0.77 [95%CI 0.55-1.08]). Results were similar by smoking status, except a non-significant 1.45-fold increased risk with ≥8 coffee cups/day for non-smokers. There was a non-significant reduced GDM risk with increasing total caffeine.

Conclusions: Our results suggest that moderate first trimester coffee and tea intake were not associated with GDM increased risk and possibly may have a protective effect.