ClinicalTrials.gov, www.clinicaltrials.com , NCT01698385.

Aims/hypothesis The aim of this study was to assess the interaction between melatonin receptor 1B gene (MTNR1B) rs10830963 polymorphism and lifestyle intervention during pregnancy on occurrence of gestational diabetes mellitus (GDM) in high-risk women. Methods This is a secondary analysis of the randomised controlled gestational diabetes prevention trial 'RADIEL', conducted between 2008 and 2014 in four maternity hospitals in southern Finland. A total of 226 women with a history of GDM and/or a pre-pregnancy BMI ≥ 30 kg/m 2 were enrolled at <20 weeks of gestation (mean 13 weeks) and randomised into an intervention group receiving counselling on diet, physical activity and weight control and a control group receiving standard antenatal care. The main outcome was incidence of GDM, defined as one or more pathological glucose values in a standard 75 g 2-h OGTT. The MTNR1B rs10830963 was genotyped for further analyses.Results No significant differences were found in the genotype distribution between the intervention and the control group. A significant interaction was observed between the rs10830963 genotypes and the lifestyle intervention on age-adjusted occurrence of gestational diabetes (p = 0.038). Among women homozygous for the C allele of rs10830963, the OR for GDM was significantly lower in the intervention group than in the control group (OR 0.

The high prevalence of impaired glucose metabolism was observed already in early pregnancy, which may have contributed to the lack of effect of the intervention.