High preconception thyroid hormone levels may lower egg count, but not IVF success

Women with higher-than-normal thyroid-stimulating hormone (TSH) levels before starting in vitro fertilization (IVF) may have fewer eggs available for treatment. But according to new research from Beijing Chao-Yang Hospital, their chances of getting pregnant or having a baby are not reduced if the thyroid condition is properly treated.

The study, published in Reproductive and Developmental Medicine, followed 1,340 women going through their first round of IVF or intracytoplasmic sperm injection (ICSI). The women were grouped by their TSH levels: normal (0.55–2.5 μIU/mL), slightly high (2.5–4.0 μIU/mL), and high (≥4.0 μIU/mL). Those in the highest group were given levothyroxine, a standard thyroid medication, to bring their hormone levels down before starting ovarian stimulation.

Researchers found that women with higher TSH levels (≥4.0 μIU/mL) had fewer antral follicles—a measure of egg reserve—and created fewer fertilized eggs, with a slightly lower fertilization rate. However, when it comes to outcomes, such as embryo quality, pregnancy rates, miscarriage risk, and live birth rates, there were no significant difference between the groups.

“Higher TSH was linked to fewer eggs, but treatment seemed to balance out pregnancy outcomes,” the authors explained. In other words, thyroid health may affect how many eggs are produced, but it does not necessarily determine whether IVF will succeed, so long as the condition is managed early.

The study also found that women with higher TSH often had less healthy cholesterol and uric acid levels, suggesting possible effects on metabolism. Still, the researchers noted that their study was based on past medical records and more clinical trials are needed to confirm these findings.