Comparison of successive pregnancies provides evidence for a maternal component in determining circulating steroid concentrations.

Maternal concentrations of steroids have been widely used to monitor fetal well-being but the tests are less discriminatory than usually required (1). Possibly some pregnant women differ from others by normally having different metabolic capability and so different expected concentrations of steroids. Plasma progesterone (average 3.5 samples per pregnancy) and estriol (4.2) were measured during two normal pregnancies of women who were both times pregnant by the same partner. Firstly, each sample concentration was calculated as a percent of the normal mean at the time of gestation, and the average of the percentages determined (for each steroid); each pregnancy was found to have higher or lower than normal values (or was of unassignable status, i.e., within 95% to 105% of the mean). For progesterone, of 13 assigned pairs, nine were of the same relativity (higher or lower status) and one was different. This difference between numbers of pairs assigned as being of the same status and of different status was statistically significant (P <0.025). For estriol of 18 pairs, 11 were the same, four different (P <0.10). Secondly, we used absolute steroid concentrations to determine the variations of concentrations relative to the means. For progesterone and estriol the variations in concentrations between two pregnancies of the same woman were much less than the variations in different women (F12,79= 7.70,P <0.001; F17,lse = 8.19, P <0.001). From these results we conclude that there appears to be a maternal contribution to concentrations attained during pregnancy of two steroids usually associated with fetoplacental production. The capability of maternal metabolism to affect concentrations in pregnancy has been preyously noted (2) without investigating, as we have done here, whether any variations were repeated in the woman’s next pregnancy.