Within our nested case–control study of
mothers giving birth in the Boston area, we
found no significant associations between
averaged or cross-sectional urinary BPA levels
and PTB when treating PTB as a single, homogeneous
outcome. After further classifying PTB
by either spontaneous or placental etiology,
no significant relationships with BPA exposure
developed, except for significantly elevated
odds of spontaneous preterm birth in association
with levels measured at visit 4 [median,
35.1 weeks (range, 33.1–38.3 weeks)].
However, these associations should be interpreted
cautiously because of the low number of
cases in each subgroup. After additional stratification
on infant sex, we observed significantly
elevated odds of overall PTB for female but not
male infants in association with averaged BPA
exposure. As far as we are aware, this is the first
study to use a more clinical and biological classification
of PTB, and to assess BPA exposure
at multiple time points during pregnancy with
regards to the risk of PTB