TOPLINE:

Hypothyroidism during pregnancy was associated with an altered metabolic profile in women with gestational diabetes. These women were more likely to test positive for anti-thyroperoxidase antibodies and had slightly higher A1c levels, with higher thyroid-stimulating hormone (TSH) levels correlating with increased A1c levels and greater insulin resistance.

METHODOLOGY:

• Investigators in France conducted a retrospective study using data from medical records to assess the association between hypothyroidism during pregnancy and metabolic parameters in 1290 women with gestational diabetes (mean age, 33 years) who had singleton pregnancies and no prior history of hypothyroidism.
• TSH levels and anti-thyroperoxidase antibodies were measured during the hospital stay after the diagnosis of gestational diabetes using an electrochemiluminescence immunoassay.
• Gestational hypothyroidism was defined as TSH levels ≥ 4 mIU/L, according to the 2017 American Thyroid Association guidelines.
• Participants were also assessed for glucose and A1c levels and for insulin resistance using the homeostatic model assessment for insulin resistance.

TAKEAWAY:

• Overall, 9% of women had hypothyroidism during pregnancy.
• Women with hypothyroidism during pregnancy were more likely to test positive for anti-thyroperoxidase antibody (16.2% vs 5.3%; P < .001) and had marginally higher A1c levels (5.35% vs 5.2%; P = .0009) than those without; these differences persisted even after adjusting for gestational age, age, ethnicity, and BMI.
• TSH as a continuous measure showed positive correlations with both A1c levels (P = .0058) and the homeostatic model assessment for insulin resistance (P = .002); these associations persisted after controlling for gestational age, age, and BMI.
• Women with vs without hypothyroidism during pregnancy were less likely to have gestational diabetes diagnosed earlier and exhibited lower fasting plasma glucose levels at early screening.

IN PRACTICE:

"We found that women with HG [hypothyroidism during gestation] displayed slightly higher HbA1c [A1c] than those without and TSH levels were positively associated with HbA1c. These findings could be explained by a synergistic effect of HG and pre-gestational insulin resistance," the investigators reported.

SOURCE:

This study was led by Sara Pinto, Assistance Publique - Hôpitaux de Paris, Avicenne Hospital, Paris 13 University, Sorbonne Paris Cité, Department of Endocrinology-Diabetology-Nutrition, Centre de Recherche en Nutrition Humaine-Ile de France (CRNH-IdF), Centre Spécialisé de l'Obésite Île-de-France Nord, Bobigny, France. It was published online on September 25, 2025, in Frontiers in Endocrinology.

LIMITATIONS:

This study was limited by its retrospective nature. Women with TSH levels ≥ 3 mIU/L after the first trimester were treated with levothyroxine, which may have precluded conclusions about untreated hypothyroidism's effect on pregnancy outcomes. This study also lacked TSH measurements throughout the first trimester.

DISCLOSURES:

This study did not receive any funding. The authors reported having no relevant conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.