September 06, 2016
2 min read

Low thyroid hormone in early pregnancy associated with risk for gestational diabetes

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In Chinese women, hypothyroxinemia was observed to be a risk factor for the development of gestational diabetes, according to results from a retrospective study.

Jianxia Fan, MD, of International Peace Maternity and Child Health Hospital and the School of Medicine at Shanghai Jiao Tong University in Shanghai, and colleagues analyzed data from 27,513 pregnant women of Chinese Han descent who underwent a first trimester antenatal screening (including measurements of thyroid-stimulating hormone, free thyroxine and thyroid-peroxidase antibody [TPOAb]) and a 2-hour, 75-g oral glucose tolerance test between 24 and 28 weeks’ gestation (abnormal glucose values were defined by American Diabetes Association criteria). Women with a personal or family history of thyroid disease, diabetes or autoimmune disease and those taking hormone therapies were excluded. Researchers used logistic regression analyses and chi-squared tests to examine the associations between free T4, TSH or TPOAb levels and incidence of gestational diabetes.

Compared with women without gestational diabetes, women with gestational diabetes were more likely to have lower levels of TSH (P = .024) and free T4 (P < .0001), whereas there were no between-group differences for TPOAb levels. After adjusting for age, BMI, delivery method, parity, family history of diabetes, and free T4 and TPOAb levels, researchers found that a TSH level of at least 1.36 mU/L was associated with a decreased risk for gestational diabetes (OR = 0.86; 95% CI, 0.76-0.97). Using free T4 levels between 9 pmol/L and 13.7 pmol/L as reference, a free T4 level of at least 14.6 pmol/L provided a protective effect against the development of gestational diabetes after adjustment (OR = 0.81; 95% CI, 0.72-0.9).

After evaluating the incidence of gestational diabetes among patients with differing levels of free T4, TSH or TPOAb, researchers found that free T4 played a role in predicting gestational diabetes, with gestational diabetes incidence decreasing as the level of free T4 rose.

Researchers also found that increasing maternal age, increasing prepregnancy BMI and a family history of diabetes were risk factors for development of gestational diabetes.

“This study provides new evidence showing that low thyroid hormone levels increase the risk for developing [gestational diabetes] in early pregnancy,” the researchers wrote. “A low [free] T4 level during early pregnancy was reciprocally associated with BMI, which to a certain extent explains why low [free] T4 levels were found to contribute to the risk for developing diabetes. Nonetheless, because the direct biological activity of [free triiodothyronine] was not measured in this study, we could [not] fully explain this phenomenon, and further study is therefore needed.” – by Regina Schaffer

Disclosure: The researchers report no relevant financial disclosures.