Frozen blastocyst transfer outcomes in immediate versus delayed subsequent cycles following GnRH agonist or hCG triggers



The aim of this study is to analyze clinical pregnancy rates (CPR) and ongoing pregnancy rates (OPR) for frozen embryo transfers (FET) performed with blastocysts in the cycle immediately after GnRH agonist (GnRHa) versus human chorionic gonadotropin (hCG) triggers, with outcomes of delayed FET for comparison.


Retrospective cohort study at a university-affiliated in vitro fertilization (IVF) clinic, including patients undergoing IVF between 2013-16 with a blastocyst FET performed within two menstrual cycles of a previous stimulation cycle and vaginal oocyte retrieval (VOR). FETs included programmed and natural endometrial preparation. Outcome measures were clinical and ongoing pregnancy rates.


CPR and OPR for 344 FET cycles were similar when comparing immediate and delayed transfer overall (crude CPR 67.5 versus 76.5%, p = 0.11; OPR 57.5 versus 66.7%, p = 0.13), and after stratifying by cycles following hCG trigger (OPR 62.5 versus 66.3%, p = 0.61) and GnRHa trigger (OPR 55.6 versus 64.5%, p = 0.17). When considering a number of predictors for OPR, an adjusted odds ratio (OR) of 1.74 [95% CI 1.00–3.03] approached significance in favor of delayed FET.


Regardless of trigger modality, patients can be reassured that pregnancy rates with FET are high in immediate and delayed cycles. However, our study suggests a potential benefit in delaying a cycle before proceeding with FET.

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We would like to thank Dr. James Grady for his consultation on the statistical analysis.


This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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Correspondence to Claudio Benadiva.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. For this type of study formal consent is not required.

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The authors declare that they have no conflict of interest.

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Kaye, L., Marsidi, A., Rai, P. et al. Frozen blastocyst transfer outcomes in immediate versus delayed subsequent cycles following GnRH agonist or hCG triggers. J Assist Reprod Genet 35, 669–675 (2018).

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  • Frozen embryo transfer
  • Ovulation induction
  • Gonadotropin-releasing hormone/agonists