Ovulatory Cycles Cut Pregnancy Loss in Embryo Transfer

Clinicians frequently evaluate different protocols to optimize endometrial receptivity before frozen-embryo transfer. Historically, programmed artificial cycles offered greater scheduling flexibility for reproductive endocrinologists. However, accumulating evidence suggests that preserving the corpus luteum confers substantial reproductive benefits. A new systematic review and meta-analysis evaluated randomized controlled trials comparing ovulatory cycles against artificial cycles.

Why Ovulation Matters in Frozen-Embryo Transfer

During natural or stimulated ovulatory cycles, the functional corpus luteum secretes essential vasoactive factors. These factors include relaxin, vascular endothelial growth factor, and endogenous progesterone. In contrast, artificial cycles replace hormones exogenously and completely lack a corpus luteum. Consequently, this absence may impair early placentation and uterine vascular remodeling. Therefore, maintaining endogenous ovarian function provides physiological advantages during early gestation.

Key Findings on Pregnancy Loss and Live Births

The systematic review analyzed 17 randomized controlled trials involving 10,611 participants. High-certainty evidence demonstrated that ovulatory endometrial preparation significantly reduced the risk of pregnancy loss by 25 percent. Furthermore, clinical pregnancy rates remained equivalent between both preparation strategies. Moderate-certainty evidence showed comparable overall live-birth rates across all pooled studies. However, sensitivity analysis excluding high-risk trials showed a 15 percent higher live-birth rate with ovulatory protocols when clinics minimized cycle cancelation.

Obstetric Safety and Clinical Implications

Beyond implantation success, the study evaluated maternal and neonatal safety outcomes. Moderate-certainty evidence indicated a clear protective trend against hypertensive disorders of pregnancy in ovulatory cycles. Additionally, researchers noted no significant difference in macrosomia rates between the study cohorts. Therefore, fertility specialists in India should prioritize ovulatory endometrial preparation in regularly cycling women. Clinicians must simultaneously optimize cycle monitoring to keep cancelation rates low.

Frequently Asked Questions

Q1: Why does ovulatory frozen-embryo transfer lower pregnancy loss rates?

Ovulatory cycles maintain an active corpus luteum that secretes vital vasoactive hormones and endogenous progesterone, which support robust early placentation.

Q2: How does endometrial preparation without ovulation affect hypertensive disorders of pregnancy?

Artificial cycles lack a corpus luteum, which may impair maternal vascular adaptation and increase the risk of gestational hypertensive disorders.

Q3: Should artificial cycles still be used for frozen-embryo transfer?

Artificial cycles remain necessary for anovulatory women, but clinicians should favor ovulatory regimens whenever patients demonstrate spontaneous or stimulated ovulation.

References

1. Martins WP et al. Endometrial preparation with vs without ovulation for frozen-embryo transfer: systematic review and meta-analysis of randomized controlled trials. Ultrasound Obstet Gynecol. 2026 Aug 25. doi: 10.1002/uog.70299. PMID: 42640814.
2. Lin YH et al. Natural Compared With Artificial Cycle Endometrial Preparation for Frozen Embryo Transfer: A Systematic Review and Meta-analysis. Obstet Gynecol. 2026;148(2):285-294.
3. Zaat TR et al. Obstetric and neonatal outcomes after natural versus artificial cycle frozen embryo transfer and the role of luteal phase support: a systematic review and meta-analysis. Hum Reprod Update. 2023;29(5):590-605.