During pregnancy, which estrogen is primarily produced as a joint effort of mother and fetus, with fetal DHEAS needed by the placenta?

• A. Estriol
• B. Estradiol
• C. Estrone
• D. Estrone sulfate

Answer: (A)

In pregnancy the main estrogen comes from a collaborative effort between the fetus and the placenta. The fetus provides DHEAS from its adrenal glands, which is then taken up by the placenta. The placental enzyme machinery converts that fetal substrate into estrogens, with estriol becoming the predominant estrogen produced. Estriol levels rise most significantly because its synthesis specifically uses fetal DHEAS, reflecting the fetal-placental unit’s activity. Estradiol and estrone are formed as well but mainly originate from maternal tissues, not from this fetal substrate in the same dominant way. Estrone sulfate is a conjugated form and does not represent the major estrogen produced during pregnancy.