Prenatal exposure to solar radiation and hypertensive disorders of pregnancy

Objective To examine the association between prenatal exposure to solar radiation and hypertensive disorders of pregnancy (HDP). Design A multicentre retrospective study. Setting 19 hospitals in the USA. Population 205 888 women with singleton gestation from the Consortium on Safe Labor (2002-2008). Main outcome measures Gestational hypertension, pre-eclampsia/eclampsia, and pre-eclampsia superimposed on chronic hypertension. Methods Medical records of the participants were linked to solar radiation obtained from the National Solar Radiation Database. Average daily solar radiation of each woman was estimated over the entire pregnancy period and over three trimesters during pregnancy according to hospital sites. Generalised estimated equation was applied to investigate the relationship between quartiles of average daily solar radiation and HDP. Restricted cubic spline was applied to assess the nonlinear associations. Results Higher average solar radiation during the entire pregnancy was associated with reduced risks of HDP. Compared with the 1st quartile of solar radiation during the entire pregnancy, odds ratios (ORs) of the 2nd, 3rd and 4th quartiles were respectively 0.80 (95% CI 0.72-0.90), 0.63 (95% CI 0.55-0.73), 0.65 (95% CI 0.54-0.78) for gestational hypertension; 0.66 (95% CI 0.57-0.76), 0.61 (95% CI 0.51-0.73), 0.77 (95% CI 0.62-0.95) for pre-eclampsia, and 0.44 (95% CI 0.36-0.55), 0.42 (95% CI 0.35-0.49), 0.60 (95% CI 0.46-0.78) for superimposed pre-eclampsia. Conclusion Exposure to higher daily solar radiation during pregnancy is associated with a decreased risk of HDP. The protective effect was stronger for superimposed pre-eclampsia than for pre-eclampsia or gestational hypertension. Tweetable abstract Exposure to higher daily solar radiation during pregnancy is associated with a decreased risk of HDP.