Estetrol

Estetrol (E4), or 15α-hydroxyestriol, is an estrogen steroid hormone, found in detectable levels in maternal serum at around week 20.

Estetrol is a human steroid, produced by the fetal liver during pregnancy only. This natural hormone was discovered in urine of pregnant women by Diczfalusy and coworkers in 1965. Estetrol has the structure of an estrogenic steroid with four hydroxyl groups which explains the acronym E4. Estetrol is synthesized in the fetal liver from estradiol (E2) and estriol (E3) by the two enzymes 15α- and 16α-hydroxylase. After birth the neonatal liver rapidly loses its capacity to synthesize E4 because these two enzymes are no longer expressed.