Thyroxine replacement during super-ovulation for in vitro fertilization: a potential gap in management?

Area of Science:

• Reproductive Endocrinology
• Thyroidology
• Assisted Reproductive Technologies

Background:

• Women undergoing in vitro fertilization (IVF) often require careful monitoring of thyroid function, especially those on thyroxine replacement therapy.
• Super-ovulation protocols in IVF involve high levels of estradiol (E2), which can impact thyroid hormone binding.
• Maintaining euthyroid status is crucial for successful conception and pregnancy outcomes.

Observation:

• Two hypothyroid women on thyroxine replacement therapy were studied during super-ovulation cycles for IVF.
• Thyroid-stimulating hormone (TSH) levels were monitored retrospectively and prospectively.
• Despite starting the cycle as euthyroid, both patients exhibited elevated TSH levels indicative of hypothyroidism during ovulation induction.

Findings:

• Elevated circulating estradiol during super-ovulation increases thyroxine-binding globulin (TBG) binding of thyroxine.
• This leads to a functional decrease in free thyroxine, resulting in increased TSH levels.
• Hypothyroidism developed during the super-ovulation cycle, even without pregnancy.

Implications:

• This suggests a potential management gap for hypothyroid women on thyroxine therapy undergoing IVF.
• Further research is needed to determine if acute biochemical hypothyroidism affects IVF outcomes (egg quality, fertilization, conception, pregnancy).
• Investigating thyroxine dose adjustments during super-ovulation cycles may be necessary to optimize IVF success rates.