Modified natural cycle for embryo transfer using frozen-thawed blastocysts: A satisfactory option

Area of Science:

• Reproductive Endocrinology and Infertility
• Assisted Reproductive Technology (ART)
• Embryology and Cryobiology

Background:

• Frozen embryo transfer (FET) is a key component of assisted reproductive technology.
• Two common protocols for FET include modified natural cycle frozen embryo transfer (NC-FET) and hormonally controlled frozen embryo transfer (HC-FET).
• Comparing the efficacy of these protocols is crucial for optimizing patient outcomes.

Purpose of the Study:

• To compare pregnancy outcomes between modified NC-FET and down-regulated HC-FET protocols.
• To evaluate the effectiveness of these protocols specifically for frozen-thawed day 5 blastocyst transfers.

Main Methods:

• Retrospective cohort study of 428 patients undergoing 493 FET cycles using frozen-thawed day 5 embryos.
• Modified NC-FET group: patients with regular menses and ovulation, triggered with hCG.
• Down-regulated HC-FET group: anovulatory or selected ovulatory patients, using medroxy-progesterone acetate, GnRH-agonist, and exogenous estradiol, followed by progesterone.

Main Results:

• No significant differences in clinical pregnancy rates (54.3% vs. 52.5%) or delivery rates (47.2% vs. 43.6%) between modified NC-FET and HC-FET.
• Logistic regression identified age, number of blastocysts transferred, and year of FET as significant factors impacting clinical pregnancy.
• No significant difference in clinical pregnancy was observed across different age groups (≤35, 36-39, ≥40).

Conclusions:

• Modified NC-FET demonstrates comparable pregnancy outcomes to down-regulated HC-FET for frozen-thawed day 5 blastocyst transfers.
• Both protocols are effective, suggesting flexibility in clinical application based on patient characteristics.
• Further research may explore specific patient subgroups that benefit more from one protocol over the other.