Season, household registry and isolated birth defects: a population-based case-control study in Danyang, China

Background A birth population-based study was conducted in Danyang, Jiangsu Province, to evaluate major birth defects in emerging regions in China with similar maternal and neonatal care conditions.Methods We conducted a population-based study in a cohort of infants born in Danyang from 2014 to 2021, including 55 709 perinatal infants. Four categories of isolated birth defects were defined as cases: congenital heart defects (CHDs; n=2138), polydactyly (n=145), cleft lip with or without palate (CL/P; n=76) and accessory auricles (n=93). Infants with congenital malformations were identified by the Chinese Birth Defects Monitoring Network.Results Compared with autumn, conception in spring (OR=1.31 [1.16-1.48]) and winter (OR=1.39 [1.23-1.58]) was associated with an increased risk of CHD. Increased risk of CHD, CL/P and accessory auricles was significantly associated with non-local registered residence (OR=1.17 [1.07-1.28], OR=2.73 [1.52-4.88] and OR=2.11 [1.20-3.71], respectively). Individuals of Han nationality were less likely to have polydactyly (OR=0.23 [0.05-0.98]).Conclusions The season of pregnancy was significantly associated with CHDs. Offspring of mothers with non-local registered hometown had greater risks of CHDs, CL/P and accessory auricles.