Maternal pregnancy estriol levels in relation to anamnestic and fetal anthropometric data

In epidemiologic studies of perinatal exposures, birth weight has been prop osed as a proxy variable for intrauterine estrogen exposure. To assess the validity of this assumption, we performed analyses of the association betwe en estriol level in 188 women in the 17th, 25th, 33rd, and 37th weeks of pr egnancy and the birth weights of their infants. We found a general increase in mean cumulative estriol dose with increasing birth weight category thro ughout pregnancy. In lace pregnancy, mean pregnancy estriol level of mother s of infants in the highest birth weight category (>4,500 gm) was twice as high as that of mothers of infants in the lowest category (<2,500 gm), 775 nmol/liter and 392 nmol/liter, respectively. Smoking lowered the maternal e striol levels by 20% or more throughout pregnancy. With smoking and birth w eight included in a regression analysis, maternal age, placental weight, an d infant ponderal index did not add any explanatory power to the model. Our data suggest that, on an aggregate level, birth weight can be used as a pr oxy variable of intrauterine estimate exposure.