Thyroid peroxidase antibodies in pregnant women with type 1 diabetes: impact on thyroid function, metabolic control and pregnancy outcome.

OBJECTIVE: In pregnant women with type 1 diabetes, we evaluated whether the presence of thyroid peroxidase autoantibodies (anti-TPO) was associated with changes in thyroid function, metabolic control and pregnancy outcome.

DESIGN/SETTING: Prospective study, Denmark.

POPULATION: Ninety-six consecutive pregnant women with type 1 diabetes. Twenty-five healthy pregnant controls.

METHODS: At 8, 14, 21, 27 and 33 weeks, the diabetic women self-monitored plasma glucose (SMPG) (8/day) for 3 days and had blood samplings obtained.

MAIN OUTCOME MEASURES: Thyroid-stimulating hormone (TSH), free thyroxin (T4), hemoglobin A1C (HbA1C), anti-TPO, pregnancy outcome.

RESULTS: Anti-TPO was detected in 31 (32%) of the pregnant diabetic women compared with two women (8%) in the healthy controls (p=0.015). The presence of anti-TPO was associated with higher TSH at 8 (p<0.0001) and 14 weeks (p<0.05) and lower free T4 at 8 weeks (p<0.05) compared with anti-TPO negative women. Twenty untreated anti-TPO positive women had higher TSH compared with untreated, anti-TPO negative women (p<0.05), but comparable free T4. At inclusion, 25% had TSH above the recommended treatment goal for levothyroxine (TSH>2.5 mIU/l), most prevalently among anti-TPO positive women. Sixteen women (17%) were treated for thyroid disorder during pregnancy. No differences were detected between the diabetic women with and without anti-TPO regarding HbA1C, insulin dose, median SMPG or pregnancy outcome.

CONCLUSIONS: Anti-TPO was present in one-third of pregnant women with type 1 diabetes and associated with slightly higher TSH, but not poorer glycemic control or adverse birth outcome. A total of 17% of women with type 1 diabetes were treated for thyroid disorder during pregnancy.