BACKGROUND
The usual treatment for hypothyroidism during pregnancy is a medication called levothyroxine, which replaces the thyroid hormone that was previously made by the thyroid. During pregnancy, the goal is to keep the TSH level below 2.5 to help protect the baby’s development. The dose of levothyroxine depends on the patient’s body weight and the cause of the thyroid problem. Past studies showed that women who were already taking thyroid medication before pregnancy usually need to increase their dose by about 30-40% once they are pregnant. A simple way to do this is by taking two extra tablets per week. This increase should happen very early in pregnancy, because the baby depends completely on the mother’s thyroid hormone during that time.

In addition to the standard tablets, levothyroxine is also available in liquid and soft-gel forms. These may be absorbed better and could be helpful during pregnancy. However, we do not have enough information about the exact dose change needed for these forms. This study was designed to compare how much levothyroxine is needed to keep the TSH below 2.5 in early pregnancy in women taking tablets versus those taking liquid or soft-gel forms.

THE FULL ARTICLE TITLE
Scappaticcio L, et al. Adjustments during pregnancy differ between users of tablet and nontablet formulation? A real-world study. Endocr Pract. Epub 2025 Dec 30:S1530- 891X(25)01350-3; doi: 10.1016/j.eprac.2025.12.021. PMID: 41478457.

SUMMARY OF THE STUDY
The study was done at a single institution. The researchers looked back at the records of pregnant women with hypothyroidism who started levothyroxine either before or during the first 3 months of pregnancy. They included patients whose TSH was within the normal range during pregnancy, had their blood test for TSH done every 30-40 days until at least 20 weeks, took their medication correctly and regularly, and did not have major pregnancy complications.

Women who had problems absorbing medications, switched between different forms of levothyroxine or gained more than 25% of their starting weight during pregnancy were not included in the study. Levothyroxine treatment was started if TSH was above 2.5 and thyroid antibodies were present, or TSH was above 4 even without antibodies. Each patient’s endocrinologist chose whether to use the tablet or liquid form. The dose was adjusted at each visit based on the test results.

A total of 335 pregnant women started treatment with levothyroxine and 212 were included in the study. About 75% had hypothyroidism before pregnancy. About 25% were diagnosed during pregnancy. In 13% of women, the cause was surgical removal of the thyroid. More women (62%) took levothyroxine tablets, while about 38% used the liquid form. Women taking the liquid form were more likely to keep their TSH levels in the target range. Both the dose and the type of formula played an important role in reaching the goal. Also, women taking the liquid form needed a lower dose to reach the target TSH, averaging 1.5 mcg/kg/day compared to the tablet 2.4 mcg/kg/day.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
In this study, liquid and soft-gel levothyroxine controlled thyroid levels better during early pregnancy and required lower doses than tablets. These forms may be especially helpful for patients with absorption problems, but dosing needs to be handled more carefully. These findings are important because if a liquid formula is used, a lower dose may be needed to avoid taking too much. Thyroid levels need to be monitored frequently, since both low and high levels during pregnancy can affect the baby.

— Ebru Sulanc, MD

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