Impact of sunshine on the risk of gestational diabetes mellitus in primiparous women.

There is a lack of data about the influence of sunshine hours on the prevalence for gestational diabetes mellitus (GDM). The aim of this study was to evaluate whether the prevalence of GDM varied according to hours of daily sunshine during the first trimester. The study cohort (N = 6189) consists of all primiparous women with a Finnish background who delivered between 2009 and 2015 living in Vantaa city, Finland. Data on births and maternal characteristics were obtained from National Health Registers. Data on sunshine hours were obtained from the Finnish Meteorological Institute. Individual daily sunshine hours during the first trimester of pregnancy were calculated for each woman. Diagnosis of GDM was based on a standard 75-g 2-h glucose tolerance test (OGTT). No relationship was observed between month of conception and GDM. Daily sunshine hours during the first trimester and GDM showed a U-shaped association (adjusted p-value 0.019). In OGTT, a U-shaped association was observed between 0-h glucose value and daily sunshine hours during the first trimester (p = 0.039) as well as with the 1-h glucose value (p = 0.012), respectively. In primiparous women daily sunshine hours during the first trimester showed a U-shaped association with the prevalence of GDM independent of pre-pregnancy risk factors.