De novo clinical hypothyroidism in pregnancies complicated by type I diabetes, subclinical hypothyroidism, and proteinuria: a new syndrome.

Fifty-one women with type I diabetes who had normal thyroxine values before becoming pregnant were evaluated. Abnormalities of thyroid tests other than thyroxine were encountered in 26 women, of whom 8 developed a low serum thyroxine level, an elevated thyroid-stimulating hormone level, and a low insulin requirement in the second trimester subsequent to an increase in 24-hour urinary protein excretion to greater than 4 gm/24 hr. Thyroid replacement led to an increase in insulin requirement to levels appropriate for gestational age. It is concluded that the woman with type I diabetes who develops proteinuria greater than 4 gm/24 hr during gestation is at risk for the development of de novo hypothyroidism during pregnancy, evidenced by a low serum thyroxine level, an elevated thyroid-stimulating hormone level, and a drop in insulin requirement.