BDNF and major depressive disorder: After adjusting for confounders, women whose serum BDNF levels were in the lowest three quartiles (≤25.31 ng/ml) had 1.61-fold increased odds (OR = 1.61; 95% CI: 1.13, 2.30) of antepartum depression as compared with women whose BDNF levels were in the highest quartile (>25.31 ng/ml).