Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
Table of Contents | PDF File for Saving and Printing

THYROID IN PREGNANCY
Low FT4and insulin needs in GDM: Causation, correlation, or confounding?

12

BACKGROUND
Thyroid hormone plays a major role in the development of the baby during pregnancy. Thyroid disorders have been associated with gestational diabetes mellitus (GDM), which is the development of diabetes during pregnancy in women who did not have diabetes before getting pregnant. The cause is thought to be related to increased insulin resistance and inflammatory pathways. Although several factors predict the need for insulin therapy in GDM, data on the impact of thyroid disorders on insulin need in GDM are limited. This study aimed to compare thyroid hormone levels between women with GDM managed with diet and lifestyle measures alone versus those requiring insulin and to determine which variables were associated with the need for insulin.

THE FULL ARTICLE TITLE
 Jelloul E, et al. Low FT4 levels in early pregnancy are associated with higher insulin therapy need in women with gestational diabetes mellitus. Eur Thyroid J 2026;15(1)

SUMMARY OF THE STUDY
This study was conducted at CHU Saint Pierre, Brussels, Belgium, from January 2013 to December 2014. Included were women with single pregnancies who underwent oral glucose-tolerance test (OGTT) screening at 24 to 28 weeks of pregnancy. Excluded were patients with preexisting diabetes, those who had conceived through in vitro fertilization, and those with multiple pregnancies.

Of 328 women diagnosed with GDM, 274 (83.5%) were treated with diet and lifestyle measures alone and 54 (16.5%) required insulin therapy. Thyroid function (TSH, FT4, TPOAb) was measured at an average of 13 weeks’ of pregnancy using center- and trimester-specific reference ranges.

The insulin therapy group had a significantly higher average BMI (28 vs. 26), higher frequency of obesity (40.7% vs. 24.8%) and fewer previous pregnancies. Prior GDM was more frequent in the insulin treated group (14.8% vs. 6.5%). TSH, TPOAb and subclinical hypothyroidism were similar between groups. Only lower FT4 levels in the group with normal BMI were independently associated with the need for insulin therapy. TSH, subclinical hypothyroidism, thyroid autoimmunity, and levothyroxine treatment (initiated before or after screening) were not associated with the need for insulin.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that women with lower FT4 levels, fewer prior pregnancies, and a history of GDM had an increased risk for the need for insulin therapy in addition to dietary and lifestyle measures for blood sugar management during pregnancy. The association between FT4 and insulin therapy was independent of thyroid autoimmunity and subclinical hypothyroidism and was most apparent in women with a normal BMI. Further studies are needed to confirm these findings and to try to better understand underlying mechanisms.

— Alan Farwell, MD

ABBREVIATIONS & DEFINITIONS

Gestational Diabetes Mellitus (GDM): the development of diabetes during pregnancy in women who did not have diabetes before getting pregnant.

Thyroxine (T4): the major hormone produced by the thyroid gland. T4 gets converted to the active hormone T3 in various tissues in the body.

TSH: thyroid stimulating hormone — produced by the pituitary gland that regulates thyroid function; also the best screening test to determine if the thyroid is functioning normally.

TPO antibodies: these are antibodies that attack the thyroid instead of bacteria and viruses, they are a marker for autoimmune thyroid disease, which is the main underlying cause for hypothyroidism and hyperthyroidism in the United States.

Table of Contents | PDF File for Saving and Printing