Objective:

To evaluate the association between urinary biomarkers of environmental chemical exposure during pregnancy and gestational length and birth weight-for-gestational-age z scores.

Approach:

• Study Design: A prospective cohort study involving 5,318 mother-child pairs from 18 US sites, with urine samples collected at a median of 25 weeks gestation.
• Analytes Measured: 113 analytes from 10 chemical classes, including phthalates, alternative plasticizers, and polycyclic aromatic hydrocarbons.
• Statistical Analysis: Models adjusted for maternal age, race and ethnicity, prepregnancy BMI, education, parity, season and year of urine collection, and tobacco use.

Key Findings:

• 110 of 113 analytes were detected in at least one sample, with 43 detected in at least half of samples.
• Phthalates and alternative plasticizers were associated with younger gestational age at birth.
• Each interquartile-range increase in summed diisononyl phthalate metabolites was linked to about 0.6 fewer days of gestation.
• Detection of phthalic acid was associated with about 1.1 fewer days of gestation.
• 15 analytes or sums from various chemical classes were associated with lower birth weight-for-gestational-age z scores.

Interpretation:

The study found associations between certain environmental chemicals, particularly phthalates, and shorter gestational length and lower birth weight-for-gestational-age z scores, but causation cannot be inferred.

Limitations:

• Observational design limits causal inference.
• Single midpregnancy urine sample may not reflect exposure throughout pregnancy.
• Site selection and urine sample criteria may affect representativeness.
• Long-term storage of urine samples could influence analyte measurement.
• Potential for false-positive and false-negative findings due to the large number of analytes.

Conclusion:

The findings indicate that exposure to certain urinary analytes, especially phthalates and alternative plasticizers, is linked to shorter gestation and lower birth weight-for-gestational-age z scores, but these are associations and do not imply causation.

Sources:

• JAMA Network Open