The ToF-study - comparing the cumulative live birth rate of blastocyst-stage versus cleavage-stage embryo transfers in good prognosis IVF patients: a multicenter randomized controlled trial

Abstract Study question Does blastocyst-stage embryo transfer in fresh and frozen cycles improve the cumulative live birth rate (cLBR) compared with cleavage-stage embryo transfer in IVF/ICSI treatments? Summary answer In good prognosis IVF patients (≥4 available embryos), a blastocyst-stage transfer policy did not result in a significant higher cLBR compared to cleavage-stage transfer policy. What is known already A recent Cochrane systematic review and meta-analysis concluded that fresh blastocyst-stage transfer in IVF/ICSI treatments is associated with higher rates of pregnancy in comparison to fresh transfer of cleavage-stage embryos. However, it is unknown whether a blastocyst-transfer policy also improves the cumulative live birth rate, i.e. the live birth rate derived from fresh and frozen-thawed embryo transfers following a single oocyte retrieval, in comparison to a cleavage-stage transfer policy in IVF/ICSI. Study design, size, duration In this multicenter randomized controlled trial women were randomly allocated to blastocyst-stage transfers (blastocyst group - fresh embryo transfer on day 5 after oocyte retrieval followed by vitrification of remnant blastocysts on day 5 and 6 following local criteria) or cleavage-stage transfers (cleavage-stage group - fresh embryo transfer on day 3 after oocyte retrieval followed by embryo cryopreservation on day 3 or 4). Randomization was stratified for age (≥36 or < 36 years). Participants/materials, setting, methods Women with a good prognosis after IVF/ICSI (defined as presenting ≥4 available embryos on day 2 of embryo culture), during their first, second, or third treatment cycle, were included. The primary outcome was the cLBR per oocyte retrieval, including associated frozen-thawed embryo transfers within 12 months after randomization (or 17 months during the COVID pandemic). Risk ratios (RR) with 95% CI adjusted for age group were calculated using log-linear binominal regression. Main results and the role of chance A total of 1202 women from 21 Dutch centers were randomly assigned to blastocyst-stage transfers (N = 599) or cleavage stage transfers (N = 603) between 2018 and 2021. At submission of this abstract, data on the primary outcome was available for 1153 (95.9%) women, 577 women in the blastocyst-stage group and 576 women in the cleavage-stage group. The cumulative live birth rate was 58.2% (336/577 women) in the blastocyst-stage group and 57.3% (330/576 women) in the cleavage stage group (RR 1.022, 95% CI 0.844-1.237; p = 0.825). The live birth rate after fresh embryo transfer was 38.0% (219/577 women) versus 29.9% (172/576 women) in the blastocyst-stage group and cleavage-stage group respectively (RR 1.282, 95% CI 1.017-1.615 p = 0.035). Interaction was found between age and day of transfer with a higher cumulative live birth rate and a higher live birth rate after fresh transfer in women of 36 years or older in the blastocyst group. Analyses on other IVF treatment outcomes, obstetrical or neonatal outcomes, patient burden, and cost effectiveness are ongoing. Limitations, reasons for caution Outcomes are only applicable for treatments of women with at least four embryos available on day two of embryo culture. Wider implications of the findings A blastocyst-stage embryo transfer policy did not result in a significant higher cumulative live birth rate in comparison to a cleavage-stage embryo transfer policy in IVF/ICSI treatments. Further research into the interaction of age with outcomes is warranted. Trial registration number NTR7034