In vitro fertilization (IVF) has significantly advanced since its inception, but many women still face challenges in achieving successful pregnancies. Women with fewer than 10 oocytes retrieved, or those with a poor ovarian reserve (defined by an antral follicle count of fewer than 5 or a serum anti-Müllerian hormone level below 8.6 pmol/L), are typically considered to have a lower chance of success.
To improve their odds, some women have turned to embryo conservation by electively freezing all embryos and planning a frozen embryo transfer (FET). Although prior studies have compared frozen versus fresh embryo transfers, there has been a lack of randomized controlled trials to provide more conclusive evidence. A recent study aimed to determine if a freeze-all strategy leads to more live births than fresh embryo transfers.
The study included women of all ages undergoing their first or second IVF cycle. Participants were randomly assigned to either the frozen embryo transfer group or the fresh embryo transfer group. The randomization process was stratified by age (under 35 or 35 and older) and study site. At each site, doctors determined the interventions, number of embryos, and regimens for each participant.
The primary outcome measured was the occurrence of a live birth at 28 weeks of gestation or later following the initial embryo transfer. A total of 838 women participated in the study, with 419 in each group.
Results showed that the fresh embryo transfer group had a higher live birth rate. Of the 419 women in the frozen embryo transfer group, 132 (32%) achieved a live birth, compared to 168 (40%) of the 419 women in the fresh embryo transfer group (relative ratio 0.79; P=0.009). The frozen embryo transfer group also had a lower pregnancy rate, with 39% (164 of 419) becoming pregnant, compared to 47% (197 of 419) in the fresh embryo transfer group (relative ratio 0.83; P=0.02). Additionally, the frozen embryo transfer group experienced a higher rate of pregnancy loss—31% (61 of 196) versus 23% (50 of 221) in the fresh group (relative ratio 1.38; P=0.05).
After one year, the cumulative live birth rate was still higher in the fresh embryo transfer group, with 51% (215 of 419) achieving a live birth, compared to 44% (185 of 419) in the frozen embryo transfer group (relative ratio 0.86; P=0.03).
In conclusion, the study found that fresh embryo transfers resulted in more live births and a higher cumulative live birth rate within one year compared to frozen embryo transfers. Based on these findings, women with a low prognosis for IVF may benefit from considering fresh embryo transfer as a better option.
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