ABSTRACT Urinary levels of estriol, estrone and estradiol-17β (estradiol) increase during the last 20 weeks of pregnancy in a qualitatively similar fashion in both the normal and diabetic states. The relative amounts of these estrogens found in the urine suggest that they arise from the same source in both groups according to the transformation, estradiol⇌estrone→estriol. It also appears likely that there is an additional source of estriol in the two groups, particularly in late pregnancy. There is a tendency for estriol levels to be lower in diabetic than in nondiabetic pregnancy. Considerable variability in the relative amounts of these 3 estrogens from one pregnancy to another, both diabetic and normal, suggests the occurrence of a varying pattern of estrogen metabolism from one individual to another. INTRODUCTION COMPLICATIONS during pregnancy in patients with diabetes mellitus, particularly the high incidence of intra-uterine death, have been recognized for some time. Despite this, little precise inf...