Maternal Age, Parity and Isolated Birth Defects: A Population-Based Case-Control Study in Shenzhen, China

Background: The etiology of birth defects has been widely studied but is not yet fully clarified, previously published data had suggested that maternal age or parity maybe involved, but without consistent conclusions. Methods: A population-based, case-control study was nested in a cohort of perinatal infants born from 2010 to 2012 in Baoan District, Shenzhen. Four categories of isolated birth defects were defined as cases: congenital heart defects (CHD, n=693), polydactyly (n=352), cleft lip with or without palate (CL/P, n=159) and equinovarus (n=119). Controls were non-malformed infants (n=11,307) randomly selected from the same area and period. Odds ratios (ORs) and the 95% confidence intervals (CIs) were computed by multivariable unconditional logistic regression analysis. Results: Young maternal age (<25 years old) was associated with a reduced risk of CHD (adjusted OR=0.73, 95% CI 0.59-0.90), while with an elevated risk of polydactyly (adjusted OR=1.42, 95% CI 1.09-1.84). Increased risk of CL/P-affected pregnancy was observed in mothers older than 35 years old (adjusted OR=2.12, 95% CI 1.26-3.57). Compared to primipara, those having their second, and third or more delivery were less likely to have infants with equinovarus, with significant adjusted ORs of 0.59 (0.40-0.89) and 0.42 (0.19-0.93), respectively. Conclusion: Maternal age was significantly associated with CHD, polydactyly and CL/P relevant pregnancy. Mothers with higher parity might have lower risk of equinovarus occurrence in offsprings.