A modified natural cycle results in higher live birth rate in vitrified-thawed embryo transfer for women with regular menstruation

ABSTRACT

There is no consensus regimen for the optimal endometrial preparation for cryopreservation and vitrified-thawed embryo transfer cycles. This is largely caused by the lack of sufficient investigation and analyses on the respective pregnancy and perinatal outcomes by different regimens. This study aimed to compare both pregnancy and perinatal outcomes between the modified natural and artificial cycles in vitrified-thawed day three embryo transfer for women with regular menstruation. A total of 1,482 vitrified-thawed day three embryo transfer cycles were reviewed including 427 modified natural cycles (NC), 132 ovulation induction cycles (OC), 794 artificial cycles (AC), and 129 GnRH agonist artificial cycles (GAC). The primary outcome that was evaluated was live birth rate. The NC regimen demonstrated a higher rate of ongoing pregnancy (43.8% vs. 30.2%, P = 0.002) and a lower rate of late abortion (2.8% vs. 14.0%, P = 0.003) than the GAC regimen as well as a higher implantation rate (31.9% vs. 27.1%, P = 0.008) and live birth rate (43.1% vs. 34.1%, P = 0.002) than the AC regimen. A significantly higher peak endometrial thickness before transfer was observed in patients using the NC and GAC regimens (10.0 ± 1.7, 9.9 ± 2.4) compared to the AC regimens (9.2 ± 1.5, P = 0.000). Multivariate logistic regression showed that the NC protocol was associated with a higher live birth rate. There were no significant differences in rates of pregnancy complications, neonatal mortality, birth defects, mean birth weight, and other perinatal outcomes among the regimens. Modified natural cycle endometrial preparation regimen for vitrified-thawed day three embryo transfer is associated with superior live birth pregnancy outcomes compared to artificial cycles. Future studies are warranted to investigate the underlying biologic mechanisms of these findings.

Abbreviations ART: assisted reproductive technology; BMI: body mass index; FET: frozen-thawed embryo transfer; HCG: human chorionic gonadotropin; IVF: in-vitro fertilization; IVF-ET: in-vitro fertilization and embryo transfer; OHSS: ovarian hyperstimulation syndrome; RCTs: randomized controlled trials

KEYWORDS:

• Day three embryo transfer
• endometrial preparation regimens
• live birth rate
• vitrification

Declaration of interests

This work was supported in part by grants from the Scientific and Technological Project of Henan Province (NO. 201203049) and the Merck Serono China Research Fund for Fertility. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.

Additional information

Notes on contributors

Xingling Wang

Conceived and designed the experiments: ZZ, XW, YG; Perform the study: YG; Acquisition of data: HF, ZX, ZL; Writing or revision of the manuscript: YG, AKS; Administrative, technical, or material support: YG, JZ, LS; Study supervision: ZZ, XW.

Zhan Zhang

Conceived and designed the experiments: ZZ, XW, YG; Perform the study: YG; Acquisition of data: HF, ZX, ZL; Writing or revision of the manuscript: YG, AKS; Administrative, technical, or material support: YG, JZ, LS; Study supervision: ZZ, XW.