A large cohort study in China identifies early pregnancy as a sensitive period when exposure to sulfur dioxide is associated with higher odds of limb abnormalities, further increasing attention to air quality and maternal health protection.

study: Maternal exposure to air pollution and risk of congenital limb defects in offspring. Image credit chayanuphol/Shutterstock

In a recent article published in a magazine scientific reportresearchers investigated whether women who were exposed to environmental air pollutants during the pre- and early pregnancy periods were more likely to give birth to children with congenital limb defects (CLD).

Researchers found that women who were exposed to sulfur dioxide during the first three months after pregnancy were more likely to have children diagnosed with certain congenital limb defects, particularly limb shortening and limb shortening. polydactyly.

Congenital limb defects and environmental risk factors

CLD A common birth defect involving missing, shortened, or abnormally formed limbs, including polydactyly (the formation of extra digits), syndactyly (webbed or fused toes and toes), shortened limbs, and clubfoot (the feet point downward at birth). These are a common type of birth defect worldwide, affecting approximately 3.9 out of every 1,000 births in China.

CLD It can have a serious impact on physical function, development, and quality of life, as well as impacting caregivers and putting a strain on the healthcare system. Although some cases can be explained by genetic or chromosomal abnormalities, about half of the cases CLD There is no clearly identified cause, highlighting the potential role of environmental factors.

Growing evidence suggests that exposure to ambient air pollution during pregnancy causes adverse pregnancy outcomes, including increased odds of certain birth defects such as facial, oral, and heart defects. However, research linking air pollution to CLD Still lacking and inconsistent. Most previous studies have relied on small case-control designs, focused on a limited range of exposures, or examined only a single contaminant.

Population-based cohort and exposure assessment

The researchers used data from the Wuhan Maternal and Child Health Management Information System, which includes detailed information on maternal, pregnancy, and birth outcomes collected through a government registration system. In addition to birth defect-related information, the dataset included sociodemographic variables, past medical history, pregnancy-related complications, pregnancy history, antenatal care utilization, delivery details, and postnatal care.

The study involved 510,550 mother-child pairs from January 2011 to September 2017. All stillbirths, live births, and abortions due to congenital abnormalities were included. Congenital limb defects were identified by a standardized birth defects surveillance system and categorized as polydactyly, syndactyly, shortened limbs, and clubfoot.

The researchers obtained daily concentrations of six major air pollutants from 21 monitoring stations across Wuhan. Individual exposure levels were estimated by incorporating the spatial distance between the monitoring station and the mother’s residential address. The exposure period included 3 months before conception and 3 months after conception.

Multivariate logistic regression models were used to assess the association between pollutant exposure and pollutants. CLD Adjust for risk and key maternal and infant characteristics. Stratified analyzes and interaction tests were conducted to explore potential effects variation by selected sociodemographic and pregnancy-related factors.

Association between pollutants and limb defects

Out of 510,550 live births, 1,864 infants were diagnosed with: CLDcorresponding to an incidence of 3.7 per 1,000 live births. Exposure to sulfur dioxide during the first three months after pregnancy was significantly associated with a higher likelihood of a child being diagnosed with some disease. CLDadjusted odds ratios ranged from 1.033 to 1.043 per 10 μg/m3 increase, indicating modest effect sizes at the individual level.

In contrast, no consistent association between overall was observed. CLD Risks and exposure to other major pollutants, such as particulate matter, nitrogen dioxide, carbon monoxide, and ozone, before or during early pregnancy. However, in subtype-specific analyses, ozone exposure during the third month of pregnancy was associated with increased odds of syndactyly.

Subgroup analyzes showed that sulfur dioxide exposure was specifically associated with higher odds of limb shortening and polydactyly, but no consistent association was observed for clubfoot. The two-pollutant model confirmed the robustness of the sulfur dioxide-related findings, and sensitivity analyzes yielded similar results even after excluding infants with additional birth defects.

Effect modification analyzes suggested a stronger association among women whose occupation was classified as professional, and variation by maternal age, timing of pregnancy, and living environment, but statistical evidence of an interaction was not uniform across all exposure windows. Limited evidence of an interaction was observed for preterm birth during specific exposure periods.

Public health implications and research limitations

Using data from a large population-based cohort, this study provides evidence that maternal sulfur dioxide exposure during early pregnancy, but not before pregnancy, is associated with higher odds of congenital limb defects, particularly polydactyly and limb shortening. Other major air pollutants, such as ozone, carbon monoxide, nitrogen dioxide, and particulate matter, were not consistently associated with overall impacts. CLD risk.

This finding is consistent with several previous studies and suggests that early pregnancy may represent a biologically plausible period of increased vulnerability to limb development. The main strengths of this study include the large sample size, population-based design, detailed exposure assessment, and consideration of multiple exposure windows and potential sociodemographic modifiers.

However, limitations include potential misclassification of exposure due to reliance on residential address and surrounding monitoring stations, lack of individual exposure measurements, and limited information on indoor air pollution and maternal behavioral factors.

Despite these limitations, this study highlights the importance of reducing pregnant women’s exposure to sulfur dioxide and considering potentially vulnerable subgroups in public health strategies. Although there are absolute risks, CLD Although still low at the individual level, this finding provides evidence that may inform environmental policy discussions and preventive efforts to reduce birth defects.