A recent study published in The BMJ suggests that fresh embryo transfer during in vitro fertilization (IVF) may enhance the chances of success for women with a low prognosis of having a healthy baby compared to frozen embryo transfer. The research aims to address gaps in understanding whether women with low prognosis benefit from fresh embryo transfers, a question that has remained unclear in IVF treatments.
In standard IVF practice, embryos are usually frozen before treatment to avoid overstimulation of the ovaries from fertility drugs. For women with a favorable prognosis, live birth rates between fresh and frozen embryo transfers are generally similar. However, this study focused on women with a lower chance of success, determined by factors like having fewer than 9 oocytes, a low antral follicle count, or a low serum anti-Müllerian hormone level.
The study included women undergoing their first or second IVF cycle with low prognosis and randomized them into two groups: fresh embryo transfer or frozen embryo transfer. The women were stratified by age (under 35 years or 35 years and older). Ovarian stimulation was performed using either a gonadotropin-releasing hormone antagonist or agonist protocol, with oocyte retrieval occurring 34 to 36 hours after human chorionic gonadotropin administration.
Embryos with 7 to 10 cells and a score of 3 or 4 were considered good quality, while blastocysts were deemed good quality if they reached an expansion stage of 4 or greater with an inner cell mass score of B or better.
The fresh embryo transfer group had their embryos transferred 3 to 5 days after oocyte retrieval, while the frozen embryo transfer group had their embryos transferred on the day of thawing. Luteal phase support was provided for women who achieved pregnancy for 10 to 11 weeks.
The primary outcome of the study was live birth after the first embryo transfer, with secondary outcomes including clinical pregnancy rates, twin live birth rates, pregnancy loss, and cumulative live birth rates. The analysis included 838 women, with 419 women in each group.
Results showed that 32% of the women in the frozen embryo transfer group achieved a live birth, compared to 40% in the fresh embryo transfer group. This indicated a difference of 8.6% and a relative risk ratio of 0.79. For secondary outcomes, fresh embryo transfer was associated with higher rates of clinical pregnancy (47% vs 39%) and cumulative live birth (51% vs 44%), but also with a higher rate of pregnancy loss (23% vs 31%).
The findings suggest that fresh embryo transfer may provide a better chance of live birth for women with a low prognosis for IVF. However, the authors also call for further research to explore strategies involving back-to-back cycles for accumulating embryos.
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