Appoximately 95% of Down syndrome (DS) cases are caused by an error in germ cell division (meiosis), resulting in an extra chromosome 21. The meiotic error, predominantly of maternal origin, occurs either during the mother's fetal life (meiosis I) or at ovulation (meiosis II). Because maternal-age-specific DS prevalence rates vary between and within populations, it has been hypothesized that environmental factors can affect the risk for a DS pregnancy.
In a population-based case-control study of 997 clinically recognized DS cases (including fetal losses) and 1007 controls without a birth defect, we examined the mother's socioeconomic status (SES) from the time of her fetal life to the time of conception. SES variables were considered as proxies for environmental factors. We used multiple logistic regression for the analyses.
We found associations with low levels of each SES variable examined: mother's education less than high school (OR, 1.29; 95% CI, 1.01–1.65), father's low occupation (OR, 1.23; 95% CI, 0.95–1.60), father's low education (OR, 1.28; 95% CI, 0.99–1.64), mother's father's low occupation (OR, 1.35; 95% CI, 1.06–1.71), and family income $820,000 (OR, 1.31; 95% CI, 1.02–1.68). The risk for DS increased as the number of low socioeconomic factors present throughout the mother's life increased. With four factors present, the risk (adjusted for confounders) almost doubled (OR, 1.98; 95% CI, 1.30–3.01). Those associations persisted among young (<30) and old (≥30) maternal age groups.
A mother's low SES during any period before conception increases her risk for a recognized pregnancy with DS. Because of the high birth prevalence of DS, the public health impact of maternal SES may be considerable. Birth Defects Research (Part A) 67:522–528, 2003. © 2003 Wiley-Liss, Inc.