Long-term prospective study of postpartum thyroid dysfunction in women with insulin dependent diabetes mellitus.

Postpartum thyroid dysfunction (PPTD) is a common autoimmune disorder. Type I diabetes mellitus (IDDM) is an autoimmune disease with a high incidence of concomitant autoimmune thyroid failure. We hypothesized that women with IDDM would have an increased incidence of PPTD. Women with IDDM in New York City, were followed prospectively during the second and third trimester of pregnancy and at 6 weeks, 3 months, 6 months, 9 months, and 1 yr postpartum. A long-term follow-up was performed at 31 months postpartum. Forty-one women with IDDM were recruited at their initial prenatal visit. Two women (4.8%) had thyroid function test abnormalities observed at screening, three (7.3%) had a spontaneous miscarriage, and eight (19.5%) women were noncompliant with follow-up. Twenty-eight women (68.2%) completed the study. Thyroid function tests and thyroid autoantibody determinations were obtained at all visits. PPTD was defined as a TSH greater than 5.0 or less than 0.2 mU/L in the postpartum period with documented normal thyroid function tests during pregnancy. The incidence of PPTD in women with IDDM was 25%. This is a 3-fold increase compared to a similar study by our group in a nondiabetic population. Forty-three percent of the women (3/7) who developed PPTD required treatment in the immediate postpartum period and at long-term follow-up. The remainder of the women with PPTD, as well as all women who did not develop PPTD were euthyroid at 31 months postpartum. Women with IDDM are at high risk for PPTD. We recommend that all women with IDDM be screened for thyroid hormonal abnormalities during pregnancy and at 3 months postpartum for postpartum thyroid dysfunction. Long-term follow-up did not reveal an increased incidence of hypothyroidism in women who did not require treatment in the first postpartum year.