Estradiol levels and estrogen receptor (ER) transcript expression in rat placentas. A, Estradiol levels in maternal serum did not show any significant changes; however, in amniotic fluid and placentas, the hormone levels increased on 21 dg compared to that on 16 dg (*P < .05). B, Percentage change in ERα and ERβ messenger RNA (mRNA) expression on 19 dg and 21 dg after normalization with the expression on 16 dg, for each gene, respectively. No significant differences between the three dgs were observed for ERα mRNA. A significant percentage change in mRNA expression of ERβ was detected on 21 dg when normalized to the expression on 16 dg (*P < .05). Note that real-time PCR (ReT-PCR) for both the genes was conducted separately. Samples were run in duplicates; data are mean ± standard error of the mean (n = 4/group).