Unconjugated oestriol in the cord blood of infants delivered by caesarean section at term.

Unconjugated oestriol levels in cord vein and artery and in retroplacental and maternal blood were measured in 43 women delivered by Caesarean section. The highest oestriol levels were found in retroplacental blood followed by decreasing levels in cord vein, cord artery, and maternal compartments respectively. A strong correlation was found between cord artery and maternal levels and significant correlations existed between cord vein and artery and maternal levels. This supports the suggestion of direct transmission of free oestriol across the placenta from the fetus into the mother.