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Review
. 2021 Jan 5;20(2):144-158.
doi: 10.1002/rmb2.12363. eCollection 2021 Apr.

Meta-analysis of the embryo freezing transfer interval

Roberto Matorras  1   2   3 , Jose Ignacio Pijoan  4 , Irantzu Perez-Ruiz  1 , Lucía Lainz  1 , Iker Malaina  4   5 , Sonia Borjaba  1
Affiliations
Review

Meta-analysis of the embryo freezing transfer interval

Roberto Matorras et al. Reprod Med Biol. .

Abstract

Background: The decision of whether frozen embryo transfer (FET) should be performed in the cycle immediately after OPU or at least one cycle later is controversial. FET could improve pregnancy rates in IVF; however, how much time is needed for the endometrium to return to optimal receptivity after ovarian stimulation is not known.

Methods: Electronic search in MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials to identify studies providing data on the influence of the interval between embryo freezing (or OPU) and FET in FET cycles published between January 1, 2007, and February 1, 2020.

Main findings: Data analyzed indicated that in the immediate FET cycles, there was a trend to an increased biochemical pregnancy rate (RR = 1.08; CI = 1.00-1.18), whereas the clinical pregnancy rate was somewhat higher, but without reaching statistical significance (RR = 1.07; CI = 0.99-1.15). The live birth rate was similar in the two groups (RR = 1.05; CI = 0.95-1.15), as was the implantation rate (RR = 0.98; CI = 0.83-1.16). Stratifying by embryo stage or FET type (freeze-all or FET after failed fresh transfer) showed no differences.

Conclusion: Systematically delaying FET does not offer benefits to IVF outcomes. In addition, immediate transfer is associated with a nonsignificant trend to better clinical pregnancy rate and it also avoids the psychological effects of prolonging the stress on prospective parents.

Keywords: IVF; delayed transfer; frozen embryo transfer; immediate transfer; pregnancy rates.

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Conflict of interest statement

Conflict of interest: Roberto Matorras, José Ignacio Pijoan, Irantzu Perez‐Ruiz, Lucía Lainz, Iker Malaina, and Sonia Borjaba declare that they have no conflict of interest. Human/animal rights: This article does not contain any studies with human and animal subjects performed by the any of the authors.

Figures

FIGURE 1
FIGURE 1
PRISMA flowchart
FIGURE 2
FIGURE 2
Comparison of (A) maternal age, (B) oocytes retrieved, and (C) embryos transferred in the immediate and delayed FET. No significant differences were observed. REML, restricted maximum likelihood
FIGURE 3
FIGURE 3
(A) Meta‐analysis of studies reporting implantation rates by FET interval. Meta‐analysis of the data from 6 included series (5 publications) that reported implantation rate as an outcome showed that there were no significant differences between immediate and delayed FETs. (B) Meta‐analysis of studies reporting biochemical pregnancy rates by FET interval. Meta‐analysis of the data from 5 publications that reported biochemical pregnancy rate as an outcome showed a RR of 1.08 (CI 1.00‐1.18) in favor of immediate FET. REML, restricted maximum likelihood
FIGURE 4
FIGURE 4
(A) Meta‐analysis of studies reporting clinical pregnancy rates by FET interval. Meta‐analysis of the data from 11 series (10 publications) that reported clinical pregnancy rate as an outcome showed that the clinical pregnancy rate was significantly increased in the immediate FET. (B) Meta‐analysis of studies reporting live birth rates by FET interval. Meta‐analysis of the data from 11 series (10 publications) that reported live birth rate as an outcome showed that there were no significant differences between immediate and delayed FETs. REML, restricted maximum likelihood
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