( ESTRONE-ESTRADIOL )
->- Pregnenolone sulfate
The fetoplacental unit and steroidogenesis. Note that estriol is the product of reactions occurring in the fetal adrenal, fetal liver, and placenta.
(Modified from Goodman HM. Basic Medical Endocrinology. New York: Raven, 1988.)
droxylation in the fetal liver and, to a lesser extent, the fetal adrenal gland. This step is followed by desulfation using a placental sulfatase and conversion by 3^-hydroxysteroid dehydrogenase to 16-hydroxyandrostenedione, which is subsequently aromatized in the placenta to estriol. Although 16-OH-DHEAS can be made in the maternal adrenal from maternal DHEAS, the levels are low. It has been estimated that 90% of the estriol is derived from the fetal 16-OH-DHEAS. Therefore, the levels of estriol in plasma, amniotic fluid, or urine are used as an index of fetal well-being. Low levels of estriol would indicate potential fetal distress, although rare inherited sulfatase deficiencies can also lead to low estriol.
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