Plasma Levels of Unconjugated Estrone, Estradiol and Estriol and of HCS Throughout Pregnancy in Normal Women

Plasma levels of unconjugated estrogens (estrone, estradiol and estriol) and of HCS were measured serially from the 5th to the 40th week of pregnancy in a group of 22 normal women. The levels of all four hormones increased regularly till the end of pregnancy. The sequential rise in plasma was estradiol and estrone followed by HCS and finally estriol at the 10th week of pregnancy. The different patterns of changes in the plasma levels were evidenced by the hormonal ratios, leading to the following observations: 1. Estrone to estradiol ratio was not constant throughout pregnancy, but showed a preferential accumulation of the reduced form by the end of pregnancy. 2. After the 8th week of pregnancy, estradiol, which was already elevated, increased less than placental HCS appearing in the circulation. 3. Estriol increased steeply after the 10th week of pregnancy. After the 12th week, this increase was steeper than those of estradiol and of HCS. 4. From the 18th to the 30th week, the levels of all 3 estrogens a...