Estriol is the most abundant estrogen during human pregnancy, it has a low estrogenic effect and its physiological role is not known. Recently it has been shown that estrogens have antioxidant and free-radical scavenging activity; in free form estrogens are lipophilic, here it is proposed that the role of estriol is to act as antioxidant at level of the developing fetal central nervous system, whose tissues are substantially lipid in nature.
Reyes-Romero MA. The physiological role of estriol during human fetal development is to act as antioxidant at lipophilic milieus of the central nervous system. Med Hypotheses. 2001 January Food and Nutrition Research Center, Faculty of Medicine, Universidad Juárez del Estado de Durango, Durango, Dgo. Mexico.