Serum levels of estrogens and of five 'steroid sensitive' proteins in early normal pregnancy.

Serum concentrations of sex hormone binding globulin (SHBG), pregnancy associated alpha 2-glycoprotein (alpha 2-PAG), caeruloplasmin (Cp), alpha 1-antitrypsin (alpha 1-At) and transferrin (Tf), unconjugated and total estrone, and unconjugated estradiol-17 beta were measured twice at a 4-5 week interval in 43 cases of early normal pregnancy (gestational weeks 6-19). Significant correlations between estrogen and protein levels in the total material were observed for all proteins except for Tf. However, within 2-week intervals of pregnancy, significant correlations were obtained only in certain intervals between estrogens on one hand and SHBG, Cp and alpha 1-At on the other. Significant correlations between rates of increase of estrogens and of proteins were obtained only at certain occasions for SHBG, Cp, Tf and alpha 1-At. The results indicate that, although estrogens may have a modulatory function in 'steroid-sensitive' protein synthesis, they are probably not the main physiological regulator.