Common chemicals linked to shorter gestation, lower birth weight

Clinical Takeaway: Clinicians should consider environmental chemical exposure as part of prenatal counseling, especially for patients asking how to reduce modifiable pregnancy risks. Practical steps include limiting use of plastic food containers with heat, reducing highly processed or packaged foods, avoiding smoke exposure, improving ventilation during cooking, and choosing fragrance-free personal care products when possible.

Gestational exposure to environmental chemicals is widespread, and new data suggest that several commonly encountered chemical classes may be associated with modest but potentially meaningful differences in birth outcomes.

In a large, diverse US cohort, researchers evaluated 113 chemicals or metabolites across 10 priority chemical classes in midpregnancy urine samples from 5,318 mother-child pairs. The chemical classes included phthalates and alternative plasticizers, bisphenols, parabens, benzophenones, insecticides, herbicides and fungicides, organophosphate esters, antimicrobials, halogenated phenols, and polycyclic aromatic hydrocarbons (PAHs).

Exposure was common. Nearly all measured chemicals were detected in at least some participants, and 43 of 113 analytes were detected in at least half of samples. The median number of detected analytes per participant was 45, underscoring that pregnant patients are typically exposed to multiple chemical classes rather than isolated compounds.

Phthalates and alternative plasticizers showed the most consistent associations with shorter gestation. For example, higher levels of summed diisononyl phthalate metabolites were associated with a 0.6-day shorter gestational age at birth and higher odds of preterm birth. Phthalates and alternative plasticizers are used in many consumer products, including plastics, food packaging, building materials, and personal care products.

Several chemical classes were associated with lower birth weight-for-gestational-age z scores, including phthalates or alternative plasticizers, PAHs, halogenated phenols, benzophenone 8, and bisphenol F. PAHs are generated by combustion and can come from sources such as traffic pollution, tobacco smoke, wood smoke, and some cooked or smoked foods.

The effect sizes for individual patients were small, but the authors noted that small shifts in gestational age or fetal growth can have meaningful population-level implications when exposures are widespread. This is particularly relevant for patients already at higher baseline risk for preterm birth or fetal growth restriction.

The findings do not prove causality and should not be used to alarm patients. Exposure was assessed using a single midpregnancy urine sample, which may not fully capture exposure across pregnancy, and many chemicals have short biological half-lives. Still, the study adds to evidence that reducing exposure to phthalates, alternative plasticizers, and PAHs during pregnancy may support healthier birth outcomes.

For clinicians, the results reinforce the value of practical, nonjudgmental counseling. Patients can be encouraged to reduce avoidable exposures where feasible, while recognizing that many environmental chemicals are difficult to avoid completely and may require broader public health and regulatory action.

Source: Buckley JP, et al. 2026 June 17. JAMA Netw Open. Gestational Exposure to 10 Classes of Priority Chemicals and Birth Outcomes in the ECHO Cohort