This study enrolled 3266 pregnant women, to explore the relationship of prenatal
phthalate exposure with the risk of
preterm birth and gestational age. All participants filled questionnaires and provided with up to three urine samples during three trimesters. Seven
phthalate metabolites in urines were measured. The incidences of very preterm, late preterm, early-term, late-term and postterm births were 0.58%, 3.52%, 24.22%, 10.53%, and 0.34%, respectively. Non-linear relationships were shown between
phthalate metabolites and gestational age. Except for
monomethyl phthalate (OR = 1.65, 95%CI = 1.17-2.34), the average concentrations of
phthalate metabolites were associated with a slightly and insignificantly increased risk of overall
preterm birth (<37+0 gestational weeks). Through a restricted cubic spline regression,
phthalate metabolites were found to be related to the risk of overall
preterm birth in a linear manner (p-value >0.05) or a non-linear manner (p-value <0.05). All curves indicated the overall
preterm birth risk rose with the increase of
phthalate metabolite concentrations. Finally, compared with full-term birth (39+0 to 40+6 gestational weeks),
phthalate metabolites were associated with the elevated risks of very preterm, late preterm and postterm births, although some relationships were not statistically significant. In conclusion, these findings suggested non-linear associations between
phthalate metabolites and gestational age. Exposure to some
phthalate metabolites was associated with increased risks of overall
preterm birth and postterm birth.