P4 and E2 concentrations. P4 and E2 concentrations in serum (A and D), cervix (B and E) and uterus (C and F). Data shown are means ± SEM of determinations in duplicate per group (n= 5 each). Means with different letters are significantly different. P values: A) a vs. b p<0.0001; B) a vs. b p=0.002; C) a vs. b p=0.042, b vs. c p=0.014, a vs. c p=0.001; F) a vs. b p=0.016.