A new meta-analysis offers crucial guidance on endometrial preparation protocols. Clinicians frequently evaluate natural cycle FET against programmed artificial cycles for reproductive care. Consequently, understanding which protocol delivers superior live-birth rates remains essential for evidence-based practice.
Comparing Protocols in Natural Cycle FET
Researchers conducted a systematic review analyzing eleven randomized controlled trials. These trials included 9,955 women aged 18 to 45 years. Specifically, natural cycle endometrial preparation demonstrated a significantly higher live-birth rate than artificial cycles. Live birth rates reached 41.5% in the natural group compared to 39.2% in the artificial group. Therefore, this finding corresponds to 43 additional live births per 1,000 women. Additionally, the number needed to treat was 23.
Clinical Subgroups and Miscarriage Outcomes
Subgroup analyses revealed notable differences between protocol types. For example, modified natural cycles showed significant benefits over artificial cycles. However, true natural cycles showed no statistically significant difference in live-birth outcomes. Furthermore, natural protocols yielded significantly lower miscarriage rates. Patients in the natural cycle group experienced a 13.4% miscarriage rate versus 17.5% in the artificial group. Consequently, preserving the corpus luteum may provide physiological advantages for early pregnancy support.
Implications for Reproductive Practice
These findings support prioritizing natural regimens for ovulatory women undergoing embryo transfer. However, artificial cycles remain necessary for anovulatory patients who cannot produce an endogenous corpus luteum. Moreover, clinicians should weigh scheduling flexibility against clinical outcomes. Therefore, individualizing treatment plans remains the best strategy for patient success.
Frequently Asked Questions
Q1: Why does natural cycle FET achieve better outcomes than artificial cycles?
Natural cycles preserve the corpus luteum, which secretes endogenous progesterone, vasoactive factors, and estrogen. Consequently, these physiological factors support optimal endometrial receptivity and early placental development.
Q2: How do modified natural cycles differ from true natural cycles in FET?
Modified natural cycles utilize an hCG trigger to precisely time ovulation and transfer. In contrast, true natural cycles rely entirely on spontaneous endogenous LH surges without trigger injections.
Q3: Which patients benefit most from artificial cycle endometrial preparation?
Artificial cycles benefit women with irregular or anovulatory menstrual cycles. Additionally, artificial cycles provide maximum scheduling flexibility for patients and fertility clinics.
References
- Lin LT et al. Natural Compared With Artificial Cycle Endometrial Preparation for Frozen Embryo Transfer: A Systematic Review and Meta-analysis. Obstet Gynecol. 2026 Aug 01. doi: 10.1097/AOG.0000000000006347. PMID: 42275665.
- Erden M et al. Optimizing natural FET protocols: key results from a meta-analysis. Hum Reprod Update. 2026.