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Thyroid Dysfunction in Early Pregnancy Raises Risk for Gestational Diabetes

Women with high thyroid-stimulating hormone levels and thyroid autoimmunity in early pregnancy have a fourfold risk for developing gestational diabetes and a threefold risk for delivering low-birth-weight neonates…. 

The negative effect of thyroid dysfunction on pregnancy and birth outcomes has been established. Using data from the Rhea study in Crete, Greece, researchers analyzed maternal serum samples in the first trimester of pregnancy of 1,170 women. They were tested for thyroid hormones (TSH, free thyroxine and free triiodothyronine) and thyroid antibodies (thyroid peroxidase antibody and thyroglobulin antibody). Thyroid function was tested at 14.1 weeks.

"The present study provides evidence that the combination of high TSH and thyroid autoimmunity in early pregnancy increases the risk of adverse birth outcomes such as gestational diabetes and low-birth-weight neonates, whereas thyroid autoimmunity increases the risk of spontaneous preterm delivery," researchers wrote.

According to data, the combination of high TSH and thyroid autoimmunity in early pregnancy was linked to a fourfold increased risk for gestational diabetes (RR=4.3; 95% CI, 2.1-8.9) and a threefold increased risk for low-birth-weight neonates (RR=3.1; 95% CI, 1.2-8) after adjustments for confounders.

Additional data indicate that women who tested positive for thyroid antibodies without elevated TSH levels in early pregnancy were also at a high risk for spontaneous preterm delivery (RR=1.7; 95% CI, 1.1-2.8), researchers wrote. However, a combination of high TSH and positive thyroid antibodies was not linked to preterm birth.

The researchers suggest that further studies are needed to fully understand the thyroid physiology during gestation to confirm adverse effects of thyroid disease on the mother and child.

This study by Karakosta et al provides evidence that, in pregnant women, the combination of high TSH and thyroid autoimmunity in early pregnancy increases the risk of adverse birth outcomes such as gestational diabetes and low-birth-weight neonates, whereas thyroid autoimmunity increases the risk of spontaneous preterm delivery.

Previously performed observational studies have not validated these results. The patients in this study seemed to have a higher likelihood of having elevated TSH levels compared to other study populations. The dietary iodine status of these women and potentially confounding medication use was unknown, making interpretation of their thyroid tests challenging. In addition, autoimmune type 1 diabetes should ideally have been ruled out, given its association with autoimmune thyroid disease.

These findings should be replicated in independent cohorts, and, if so, can have implications regarding universal screening and treatment of thyroid disease during pregnancy, in an effort to reduce preventable complications.

Karakosta P. J Clin Endocrinol Metab. 2012;doi:10.1210/jc.2012-2540.