Comparing pregnancy outcomes between natural cycles and artificial cycles following frozen‐thaw embryo transfers

Abstract

Background: Frozen embryo transfer (FET) is increasing in prevalence. In contrast to the amount of research performed on the actual cryopreservation procedure, there are limited data with respect to optimal endometrial preparation in FET cycles. Increasingly artificial cycle (AC) preparation is being adopted over the natural cycle (NC) to facilitate greater access to FET. However, there remains a paucity of data comparing pregnancy outcomes between these two commonly used cycle types. Aims: To examine the efficacy of AC vs NC following FET, by comparing pregnancy outcomes including biochemical, clinical and live birth rates, along with miscarriage rates. Materials and Method: This is a large single-centre retrospective analysis, examining a standardised data set from January 2015 to July 2018. It included 3030 cycles (NC = 2033, AC = 997). Main outcomes were biochemical pregnancy (betahuman chorionic gonadotropin > 5 IU), ultrasound-diagnosed clinical pregnancy, and live births. Using the χ 2 test, the above pregnancy outcomes were compared between AC and NC. A multivariate logistic regression, controlling for factors such as age, embryo quality, and day of blastocyst freeze was further utilised to assess for confounding variables. Results: No difference was observed between biochemical pregnancy rates (NC = 39.45% vs AC = 37.71%, P = 0.357); statistically significant differences were observed between clinical pregnancy (30.84% vs 26.08%, P = 0.007), and live birth rates (24.40% vs 18.86% P = 0.001). Multivariate analysis confirmed that NC produces superior pregnancy outcomes when controlling for confounding variables. Conclusion: This analysis demonstrates the non-inferiority of NC thaw compared to AC, on continuing pregnancy rates. Taken together with patient acceptability and possibly increased obstetric risks with AC, these findings support the use of NC when medically possible.

Treatment outcomes of blastocysts thaw cycles, comparing the presence and absence of a corpus luteum: a systematic review and meta-analysis

“…A recent large retrospective study by Pakes et al which analysed blastocyst thaw cycles, observed that the AC group experienced a higher pregnancy loss compared with the women in the NC group. 10 In this study, women in the AC group were significantly younger and received a higher proportion of good quality day-5 blastocysts compared with the NC which may have biased results to favour the AC, however, the AC group still demonstrated more pregnancy losses compared with the NC group.…”

“…We included nine studies in our final quantitative analysis. 10 16 20–26 Two of which were RCTs 22 23 both of which studied small sample sizes. The remaining seven were retrospective cohort studies, 10 16 20 21 24–26 which followed a much larger sample size.…”

“…A summary of the studies included in the meta-analysis can be found in table 1 . The largest study included 3030 cycles by Pakes et al , 10 and the smallest study included 116 cycles by Sheikhi et al . 23 …”

“…Previous studies have found that treatment outcomes of tNC and ACs have been comparable 7–9. Some studies, however, have noted that thaw cycles without a CL may have experienced higher rates of early pregnancy loss 4 10 11. This review aimed to explore these findings further.…”

Impact of frozen thawed embryo transfer in hormone substituted cycles on thrombotic risk markers

“…both demonstrated non-inferiority in the NC-FET group compared to the AC-FET group [36,37]. As the group of women having AC could differ in cycle regularity, Cochrane (Ghobara et al, 2017) compared different protocols for FET for women with regular menstrual cycles and reported no differences in live birth rates or miscarriages between the two protocols [13].…”