PBDE levels (A) and ratios (B) across maternal-placental-fetal biological matrices during mid-gestation (study waves 3 and 4; 2014–16; n = 180). Wet-weight units expressed as ng/g in fetal liver and placenta and ng/ml in maternal serum. Lipid-adjusted units expressed as ng/g lipid in all biological tissues. BDE-28 detected in only 16% of maternal serum samples. P-values < 0.05 in (A) from ANOVA test of group mean differences on log scale using censored maximum likelihood regression models. Dashed line represents PBDE level ratio equal to one between biological tissues.