The effect of an immediate frozen embryo transfer following a freeze-all protocol: a retrospective analysis from two centres.

STUDY QUESTION: Does the timing of the first frozen embryo transfer (FET) after gonadotropin-releasing hormone (GnRH) agonist triggering with the elective cryopreservation of all embryos affect pregnancy outcome? SUMMARY ANSWER: FETs performed immediately after a freeze-all cycle did not vary significantly from delayed FETs in terms of pregnancy rates. WHAT IS KNOWN ALREADY: As interest in, and use of, the freeze-all strategy expands in the field of reproductive medicine, the optimal timing to perform the subsequent FET has become increasingly important. Thus far, all clinical trials evaluating the efficacy of the segmentation strategy have opted to electively defer the first FET for at least one menstrual cycle. However, this mere empirical approach may cause unnecessary distress to infertile patients eager to conceive as soon as possible. STUDY DESIGN, SIZE AND DURATION: This retrospective cohort study included the first FET cycle of all women who underwent a freeze-all protocol between October 2010 and October 2015 in two reproductive medicine centres (in Belgium and Vietnam, respectively). PARTICIPANTS/MATERIALS, SETTING AND METHODS: A total of 333 FET cycles were included in the analysis. Following the freeze-all cycle, the preparation of the endometrium consisted of the sequential administration of oestradiol valerate and micronized vaginal progesterone. The start of the FET was classified as either immediate (following the GnRH agonist withdrawal bleeding) or delayed (by at least one menstrual cycle). Clinical pregnancy rate (CPR) was the main outcome of our study. MAIN RESULTS AND THE ROLE OF CHANCE: Women in the immediate FET group were slightly younger on average (30.9 ± 4.1 versus 31.8 ± 4.3, P = 0.045) on the date of oocyte retrieval. Moreover, women in the immediate FET group received a blastocyst transfer more frequently (53.4% versus 41.6%, P = 0.038) and had fewer embryos transferred on average compared to the delayed FET group (1.8 ± 0.8 versus 2.0 ± 0.8, P = 0.013). CPR/FET was marginally significantly higher in the immediate FET group in our crude analysis (52.9% after immediate FET versus 41.6% after delayed FET, P = 0.046). In order to assess if CPR/FET remained unaltered after adjusting for measured confounding, we performed mixed-effects multivariable regression analysis. Timing of the FET no longer affected significantly the CPR of the first FET in the adjusted analysis (adjusted odds ratio (aOR): 0.62, 95% CI: 0.38-1.00; predicted CPR of 52.5% for immediate FET versus 41.8% for delayed FET). LIMITATIONS, REASONS FOR CAUTION: The results are limited by the retrospective design and the potential for unmeasured confounding. Furthermore, we only evaluated the effect of the FET timing of the first FET on CPRs in artificially supplemented cycles and, thus, the results should not be extrapolated to live birth rates or natural-cycle FETs. WIDER IMPLICATIONS OF THE FINDINGS: This study offers a simple but potentially relevant measure to increase patient satisfaction and adherence in couples who seek to become pregnant both safely and as soon as possible. STUDY FUNDING/COMPETING INTERESTS: No funding was received for this study. The authors have no conflicts of interest to declare.

To delay or not to delay a frozen embryo transfer after a failed fresh embryo transfer attempt?

OBJECTIVE: To evaluate if increasing the interval between a failed fresh embryo transfer and a subsequent frozen embryo transfer (FET) cycle has any effect on clinical pregnancy rates (CPRs). DESIGN: Retrospective cohort study. SETTING: University-based tertiary referral center. PATIENT(S): Women who underwent at least one FET after ovarian stimulation for in vitro fertilization (IVF) and a failed fresh embryo transfer attempt from January 2010 to November 2014. We divided our sample according to the "timing" of the first FET (TF-FET), defined by the interval between oocyte retrieval and the FET cycle start date. The start of the FET was classified as either immediate (≤22 days after oocyte retrieval) or delayed (>22 days after oocyte retrieval). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): CPR after the first FET. RESULT(S): A total of 1,183 FET cycles (performed in 1,087 women) were included in our study. No significant differences were found between the immediate and delayed FET groups regarding age, number of oocytes retrieved, number of good-quality embryos produced, embryo developmental stage at FET, and number of frozen embryos transferred. Most importantly, the CPRs of the first FET did not differ significantly according to the TF-FET (32.5% after immediate FET vs. 31.7% after delayed FET), even after adjusting for potential confounding with the use of multivariable logistic regression. CONCLUSION(S): FETs performed immediately after fresh IVF cycles had CPRs similar to those postponed to a later time. Therefore, deferring FETs may unnecessarily prolong time to pregnancy.