One Plus One is Better than Two: An Approach Towards a Single Blastocyst Transfer Policy for All IVF Patients

OBJECTIVE

 It is known that the single embryo transfer (SET) is the best choice to reduce multiples and associated risks. The practice of cryopreserving all embryos for posterior transfer has been increasingly performed for in vitro fertilization (IVF) patients at the risk of ovarian hyperstimulation syndrome or preimplantation genetic testing for aneuploidy. However, its widespread practice is still controverse. The aim of this study was to evaluate how effective is the transfer of two sequential SET procedures compared with a double embryo transfer (DET) in freeze-only cycles.

METHODS

 This retrospective study reviewed 5,156 IVF cycles performed between 2011 and 2019, and 506 cycles using own oocytes and freeze-only policy with subsequent elective frozen-thawed embryo transfers (eFET) were selected for this study. Cycles having elective SET (eSET, n = 209) comprised our study group and as control group we included cycles performed with elective DET (eDET, n = 291). In the eSET group, 57 couples who had failed in the 1^st eSET had a 2^nd eFET, and the estimated cumulative ongoing pregnancy rate was calculated and compared with eDET.

RESULTS

 After the 1^st eFET, the ongoing pregnancy rates were similar between groups (eSET: 35.4% versus eDET: 38.5%; p = 0.497), but the estimated cumulative ongoing pregnancy rate after a 2^nd eFET in the eSET group (eSET + SET) was significantly higher (48.8%) than in the eDET group (p < 0.001). Additionally, the eSET + SET group had a 2.7% rate of multiple gestations, which is significantly lower than the eDET group, with a 30.4% rate (p < 0.001).

CONCLUSION

 Our study showed the association of freeze-only strategy with until up to two consecutive frozen-thawed eSETs resulted in higher success rates than a frozen-thawed DET, while drastically reducing the rate of multiple pregnancies.

Pro: Fresh versus frozen embryo transfer. Is frozen embryo transfer the future?

Embryo cryopreservation has been an integral part of ART for close to 40 years and vitrification has boosted overall ART efficacy and safety. Recently, there has been a vivid scientific discussion on whether elective cryopreservation of all embryos (freeze-all) should be pursued for most patients, with a fresh embryo transfer taking place only in selected cases. In terms of efficacy, the available evidence suggests that the freeze-all strategy leads to higher live birth rates after the first embryo transfer compared to the conventional strategy in high responders, while there is no difference in normal responders. There is no evidence to suggest that the freeze-all strategy is inferior to the conventional strategy of fresh transfer when comparing cumulative live birth rates using data from all available randomized controlled trials. The incidence of ovarian hyperstimulation syndrome is significantly reduced in the freeze-all policy. However, regarding obstetric complications and neonatal outcomes, the evidence suggests that each strategy is associated with certain risks and, therefore, there is no approach that could be unequivocally accepted as safer. Similarly, limited evidence does not support the notion that patients would be universally against freeze-all owing to the inevitable delay in pregnancy achievement. Finally, the cost-effectiveness of freeze-all is likely to vary in different settings and there have been studies supporting that this policy can be, under certain conditions, cost-effective. Adoption of the freeze-all policy can also allow for more flexible treatment strategies that have the potential to increase efficacy, reduce cost and make treatment easier for patients and clinics. Importantly, freeze-all does not require the use of any experimental technologies, further training of personnel or the costly acquisition of new equipment. For these reasons, transitioning to the freeze-all policy for most patients appears to be the next logical step in ART.

Association between the number of top-quality blastocysts and live births after single blastocyst transfer in the first fresh or vitrified-warmed IVF/ICSI cycle

RESEARCH QUESTION

Is there an association between the total number of top-quality blastocysts (TQB) developed in the first IVF/intracytoplasmic sperm injection cycle (ICSI) and live births after a single blastocyst transfer (SBT)?

DESIGN

Pregnancy outcomes from 1336 infertile women who had undergone their first IVF/ICSI treatment and accepted a first-time embryo transfer with a single fresh or vitrified-warmed blastocyst between January 2016 and August 2018 were assessed retrospectively. The restricted cubic splines method was used to evaluate the association between the number of TQB, and ongoing pregnancies and live births.

RESULTS

A significant non-linear functional form was found between the number of TQB and the ongoing pregnancies and live births (P < 0.05). The odds of an ongoing pregnancy or live birth were similar, at about 11% or higher for each additional TQB up to five TQB (odds ratio [OR] 1.11; 95% confidence interval [CI] 1.01-1.21). After this, pregnancy outcomes nearly plateaued, indicating that the number of TQB was not related to pregnancy when it was greater than five.

CONCLUSIONS

The quantity of TQB available for transfer or cryopreservation can provide important predictors for pregnancy and live birth after the first embryo transfer cycle with a single blastocyst. This valuable information may assist with the future application of SBT.

Cumulative live birth rates following a 'freeze-all' strategy: a population-based study

STUDY QUESTION

What is the cumulative live birth rate following a 'freeze-all' strategy compared with a 'fresh-transfer' strategy?

SUMMARY ANSWER

The 'freeze-all' strategy resulted in a similar cumulative live birth rate as the 'fresh-transfer' strategy among high responders (>15 oocytes retrieved) but did not benefit normal (10-15 oocytes) and suboptimal responders (<10 oocytes).

WHAT IS KNOWN ALREADY

Frozen-thawed embryo transfer is associated with a decreased risk of adverse obstetric and perinatal outcomes compared with fresh embryo transfer. It is unclear whether the 'freeze-all' strategy should be offered to all women undergoing ART treatment.

STUDY DESIGN SIZE DURATION

A population-based retrospective cohort study using data collected by the Victorian Assisted Reproductive Treatment Authority. This study included 14 331 women undergoing their first stimulated ART cycle with at least one oocyte fertilised between 1 July 2009 and 30 June 2014 in Victoria, Australia. Demographic characteristics, type of ART procedures and resulting pregnancy and birth outcomes were recorded for the stimulated cycle and associated thaw cycles until 30 June 2016, or until a live birth was achieved, or until all embryos from the stimulated cycle had been used.

PARTICIPANTS/MATERIALS SETTING METHODS

Women were grouped by whether they had undergone the 'freeze-all' strategy (n = 1028) where all embryos were cryopreserved for future transfer, or the 'fresh-transfer' strategy (n = 13 303) where selected embryo(s) were transferred in the stimulated cycle, and remaining embryo(s) were cryopreserved for future use. A discrete-time survival model was used to evaluate the cumulative live birth rate following 'freeze-all' and 'fresh-transfer' strategy.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 1028 women undergoing 'freeze-all' strategy and 13 303 women undergoing 'fresh-transfer' strategy had 1788 and 22 334 embryo transfer cycles resulting in 452 and 5126 live births, respectively. Most women (61.3%) in the 'freeze-all' group had more than 15 oocytes retrieved in the stimulated cycle compared with 18.1% of women in the 'fresh-transfer' group (P < 0.001). For high responders (>15 oocytes), the cumulative live birth rate in the 'freeze-all' group was similar to the 'fresh-transfer' group (56.8% vs. 56.2%, adjusted hazard ratio (AHR) 0.90, 95% CI 0.77-1.04). However, the likelihood of a live birth was lower in the 'freeze-all' group compared with the 'fresh-transfer' group among normal responders (10-15 oocytes) (33.2% vs. 46.3%, AHR 0.62, 95% CI 0.46-0.83) and suboptimal responders (<10 oocytes) (14.6% vs. 28.0%, AHR 0.67, 95% CI 0.14-1.01). During the minimum follow-up time of 2 years, 34.1%, 24.4% and 8.4% of suboptimal, normal and high responders, respectively, in the 'freeze-all' group did not return for any embryo transfer after the stimulated cycle, whereas all women in the 'fresh-transfer' group had at least one embryo transferred in the stimulated cycle.

LIMITATIONS REASONS FOR CAUTION

A limitation of this population-based study is the lack of information available on clinic-specific protocols for the 'freeze-all' strategy and the potential impact of these on outcomes. Data were not available on whether the 'freeze-all' strategy was used to prevent ovarian hyperstimulation syndrome (OHSS).

WIDER IMPLICATIONS OF THE FINDINGS

This study presents population-based evidence on clinical efficacy associated with a 'freeze-all' and 'fresh-transfer' strategy. The 'freeze-all' strategy may benefit some subgroups of patients, including women who are high responders and those who are at risk of OHSS, but should not be offered universally. Clinicians should consider the potential impact of electively deferring embryo transfer on treatment discontinuation in choosing the optimal embryo transfer strategy for couples undergoing ART treatment.

STUDY FUNDING/COMPETING INTERESTS

No specific funding was received to undertake this study. There is no conflict of interest, except that M.B. is a shareholder in Genea Ltd.