Purpose: To determine if blastocyst transfer increases the ongoing and cumulative pregnancy rates, compared with day 3 embryo transfer, in women of all ages when at least 4 zygotes are obtained.
Methods: Prospective study including patients undergoing a first IVF/ICSI treatment and assigned to cleavage stage (n = 46) or blastocyst (n = 58) embryo transfer. Supernumerary embryos were vitrified and patients failing to achieve an ongoing pregnancy after fresh embryo transfer would go through cryopreserved cycles. The main outcome measure was the ongoing pregnancy rate after the fresh IVF/ICSI transfer and the cumulative ongoing pregnancy rate. Results were also analyzed according to age (under 35 and 35 or older).
Results: A majority of patients (96.6 %) had a blastocyst transfer when at least 4 zygotes were obtained. The ongoing pregnancy rate was significantly higher in the day-5 group compared with the day-3 group (43.1 % vs. 24 %, p = 0.041). The cumulative ongoing pregnancy rate was higher (but not significantly) with blastocyst than with cleavage stage embryos (56.8 % vs. 43.4 %, p = 0.174). When analysed by age, patients 35 or older showed significantly higher ongoing pregnancy rate (48.4 % vs. 19.3 %, p = 0.016) and cumulative ongoing pregnancy rate (58 % vs. 25.8 %, p = 0.01) in the day-5 group compared to the day-3 group, while no such differences were observed in women under 35.
Conclusions: Blastocyst transfer can be suggested whenever there are at least 4 zygotes. While there are no differences in women under 35, the benefit of this option over cleavage stage transfer could be significant in women 35 or older.