A major international study has found that pregnant women exposed to higher levels of a persistent industrial chemical known as PFOS — a member of the PFAS “forever chemicals” group — tend to give birth to slightly smaller babies. The research, published in Nature’s Journal of Exposure Science & Environmental Epidemiology in August 2025, suggests a consistent link between maternal PFOS concentrations and reduced birth weight, adding to growing evidence that PFAS pollution poses a threat to human health even at low exposure levels.
PFOS (perfluorooctane sulfonic acid) was widely used in firefighting foams, stain-resistant fabrics, and nonstick coatings before being phased out or restricted in many countries. Yet because the compound breaks down extremely slowly, it remains detectable in water, soil, wildlife, and human blood across the globe.
Researchers led by J.M. Wright and colleagues conducted a large-scale systematic review and meta-analysis of 53 studies encompassing tens of thousands of mother-infant pairs from multiple regions. Their goal was to quantify how maternal or neonatal PFOS levels relate to birth outcomes. After screening studies published up to April 2024, the team applied rigorous statistical models to integrate the data.
The findings were strikingly consistent: for every one-unit increase in the natural log (ln) of PFOS concentration measured in maternal or newborn samples, birth weight decreased by about 30 grams (95% confidence interval: –41.6 to –18.9 g). Although a 30-gram reduction may sound small, researchers note that such shifts at the population level could have meaningful public-health implications, especially given the widespread prevalence of PFAS exposure.
Further subgroup analyses showed that the negative association persisted across study quality categories, sample timing (early pregnancy, late pregnancy, or post-delivery), and geographic regions. Medium-quality studies showed the greatest estimated reduction (around –36 g), while high- and low-quality studies reported similar declines of –28 g and –27 g respectively. The authors also performed meta-regression analyses to explore potential sources of heterogeneity — such as maternal age, gestational week, or sample type — but none explained away the observed relationship.
According to the paper, these consistent findings strengthen the evidence that PFOS exposure contributes to subtle but measurable effects on fetal growth. The study emphasizes that even though PFOS production has been curtailed, its long-lasting environmental persistence means that exposure remains a global concern.
“Each additional unit of PFOS exposure may not seem dramatic in isolation,” the authors wrote, “but across entire populations, these cumulative differences in fetal growth could translate into substantial public-health burdens.” They call for more longitudinal studies measuring PFAS levels throughout pregnancy to better understand exposure timing, biological mechanisms, and potential long-term developmental effects.
The study also highlights policy implications. Regulators in Europe and the United States have begun setting drinking-water limits for certain PFAS compounds, including PFOS, but the authors suggest that broader chemical class-based restrictions may be warranted. Improved biomonitoring and international data sharing could help identify vulnerable populations and track the effectiveness of mitigation efforts.
Experts not involved in the research note that this meta-analysis adds a critical quantitative layer to previous observational findings, making the case for urgent action on PFAS contamination stronger than ever.
Citation:
Wright J.M. et al. (2025). Birth weight in relation to maternal and neonatal biomarker concentration of perfluorooctane sulfonic acid: a meta-analysis and meta-regression from a systematic review. Journal of Exposure Science & Environmental Epidemiology (Nature). https://www.nature.com/articles/s41370-025-00798-8
