Seasonal and geographic patterns of gastroschisis in Canada: protective effect of periconceptional sunlight exposure

BackgroundGastroschisis is a right−sided, full−thickness defect with extra-amnionic herniation of abdominal contents directly into the amniotic cavity. The causes of gastroschisis remain obscure. We hypothesized that limited periconceptional sunlight exposure might lead to insufficient vitamin D during fetal development and play a role in gastroschisis etiology.MethodsWe conducted a population-based cohort study of infants conceived in Canada between April 2006 and March 2020. We used winter months (i.e., November and December) and northern geographic latitudes as indicators of insufficient sunlight exposure, while summer months (July and August) and southern geographic latitudes were considered as reference. We examined the association of conception month and geographic region with infant gastroschisis using log-binomial regression with a Poisson distribution.ResultsPrevalence of gastroschisis varied substantially by month of conception. The rate of gastroschisis for infants conceived in winter months (4.6 per 10 000) was higher than infants conceived in summer months (2.7 per 10 000; p<0.001), yielding an adjusted rate ratio (aRR) of 1.73 [95% confidence interval (CI) 1.39-2.16]. Gastroschisis prevalence increased from 2.9 per 10000 in the lowest latitude (South) to 10.8 in the highest latitude (far North) (aRR 1.89, 95% CI 1.34-2.67). Multivariate regression model showed that seasonal variations in gastroschisis risk varied with rural vs urban residence (aRR 0.68, 95% CI 0.46-0.99; p<0.05).ConclusionsOur findings indicate that periconceptional exposure to sunlight may protect against gastroschisis in offspring. Some literature inconsistencies about hypovitaminosis D and gastroschisis are clarified by interpreting associations as a non-monotonic (inverted U-shaped) relationship between maternal vitamin D status and the risk of gastroschisis. Further studies are warranted to identify biological mechanisms linking hypovitaminosis D with gastroschisis.