Frozen blastocyst transfer increases likelihood of live births
Women undergoing in vitro fertilization (IVF) with frozen single blastocyst transfer may achieve a higher rate of live birth, particularly singleton, compared with fresh single blastocyst transfer, according to a recent study.
Researchers of this multicentre, non-blinded trial evaluated 1,650 ovulatory women aged 20–35 years with regular menses who underwent a first cycle of IVF at 21 academic fertility centres in China. Participants were randomized to undergo either frozen (n=825) or fresh (n=825) single blastocyst transfer. All patients were given a gonadotropin-releasing hormone antagonist regimen for ovarian stimulation. [Lancet 2019;doi:10.1016/S0140-6736(18)32843-5]
Women in the frozen single blastocyst transfer group had a significantly higher rate of singleton live birth compared with women in the fresh single blastocyst transfer group (50.4 percent vs 39.9 percent, relative risk [RR], 1.26; p<0.0001), which according to the researchers, “was mainly mediated by a higher rate of implantation”.
Implantation rates were significantly higher among women who underwent frozen blastocyst transfer than those who had fresh blastocyst transfer (62.5 percent vs 48.7 percent, RR, 1.28; p<0.0001). “The better embryo selection by extended culture to blastocyst could … have contributed to the increased implantation rate compared with cleavage-stage embryo transfer,” noted the researchers.
The total live birth rate was also higher in the frozen blastocyst transfer group than the fresh blastocyst transfer group (53.2 percent vs 41.3 percent, RR, 1.29; p<0.0001), while the rate of twin live birth was numerically but not significantly higher in the frozen blastocyst transfer group (2.8 percent vs 1.5 percent, RR, 1.92; p=0.06).
The rate of clinical and ongoing pregnancies was also higher with frozen vs fresh blastocyst transfer (62.1 percent vs 48.6 percent, RR, 1.28; p<0.0001 and 55.5 percent vs 43.0 percent, RR, 1.29; p<0.0001, respectively).
The rate of pregnancy loss was comparable between the frozen and fresh blastocyst transfer groups (13.5 percent vs 14.0 percent, RR, 0.97; p=0.83), as was the risk of moderate or severe ovarian hyperstimulation syndrome (0.5 percent vs 1.1 percent, RR, 0.44; p=0.16).
However, a significantly higher risk of pre-eclampsia was observed in women who had frozen blastocyst transfer than fresh blastocyst transfer.
“[This] was consistent with our previous findings from a randomized trial in women with PCOS,” the researchers said. [N Engl J Med 2016;375:523-533]
“Nonetheless, there are practice changing implications to our findings. Our results suggest that frozen single blastocyst transfer is better to achieve singleton live birth than fresh single blastocyst transfer in women with good prognosis,” said the researchers, who suggested that “the increased risk of [maternal] pre-eclampsia after [a] frozen blastocyst transfer warrants further studies”.