Thyroid function in early pregnancy following frozen embryo transfer: analysis from a randomized controlled trial

Area of Science:

• Reproductive Endocrinology
• Maternal-Fetal Medicine
• Thyroid Physiology

Background:

• Thyroid function is crucial during pregnancy.
• Frozen embryo transfer (FET) protocols vary, potentially influencing maternal endocrine status.
• Understanding the impact of different FET regimens on thyroid function is essential for optimizing outcomes.

Purpose of the Study:

• To compare the effects of modified natural, programmed, and gonadotrophin-stimulated frozen embryo transfer cycles on maternal thyroid hormone levels.
• To assess the impact of these FET regimens on neonatal thyroid function.
• To provide evidence-based insights into the endocrine safety of different FET protocols.

Main Methods:

• Secondary analysis of a randomized controlled trial involving 251 women undergoing FET.
• Categorization into ovulatory (modified natural vs. programmed) and anovulatory (gonadotrophin-stimulated vs. programmed) groups.
• Measurement of maternal thyroid-stimulating hormone (TSH), free thyroxine (fT4), total thyroxine (tT4), and total triiodothyronine (tT3); neonatal TSH via screening.

Main Results:

• Programmed cycles showed significantly higher maternal tT3 and tT4 during preparation and early pregnancy.
• Elevated maternal fT4 was observed in programmed vs. modified natural cycles, but not vs. gonadotrophin-stimulated cycles.
• Maternal and neonatal TSH levels were comparable across all studied FET regimens.

Conclusions:

• Programmed FET cycles lead to higher maternal thyroxine levels but do not adversely affect maternal or neonatal TSH.
• These findings suggest that programmed FET cycles are endocrinologically safe for both women and their newborns.
• Reassuring evidence supports the endocrine health of individuals conceiving via programmed FET cycles.