Maternal oestriol levels reflect placental function rather than foetal function.

We have examined the relationship between foetal levels of E3 and DHEA-SO4 and the birthweight of the child. Levels of these steroids do not relate to birthweight--although the concentration of DHEA-SO4 was marginally but not significantly higher in infants of lower birthweight. These findings suggest that the placental conversion of foetal precursors, and not the level of the precursors themselves, determines the concentration of E3 in the mother. Measurement of E3 as a clinical test reflects the function of both the foetus and the placenta.