A recent study published in The BMJ suggests that fresh embryo transfer during in vitro fertilization (IVF) might increase the chances of success for women with a low likelihood of having a healthy baby compared to using frozen embryos.
In standard IVF treatment, embryos are usually frozen before the procedure. This prevents overstimulation of the ovaries, which can happen when fertility drugs are used alongside fresh eggs. For women with a good prognosis, the live birth rates are similar whether using fresh or frozen embryos. However, it has been unclear whether women with a lower prognosis benefit from this approach, prompting researchers to investigate further.
The study included women undergoing their first or second IVF cycle who had a low prognosis. This was defined by having nine or fewer oocytes, an antral follicle count of fewer than five, or a serum anti-Müllerian hormone level below eight. Women who were unsuitable for fresh embryo transfer or were undergoing natural cycles for oocyte retrieval were excluded.
The participants were randomly assigned to either the frozen or fresh embryo transfer group, with an equal distribution by age (under 35 or 35 and above). The ovarian stimulation protocol involved using either a gonadotrophin-releasing hormone antagonist or agonist. Oocyte samples were retrieved 34 to 36 hours after administration of human chorionic gonadotrophin.
Embryos were classified as good quality if they had 7 to 10 cells and a morphological score of 3 or 4. For blastocysts, good quality was determined by reaching an expansion stage of 4 or more and a score of B or higher for the inner cell mass.
In the fresh embryo transfer group, the transfer occurred 3 to 5 days after oocyte retrieval. In the frozen embryo transfer group, the transfer was done on the day the embryos were thawed. Women who became pregnant received luteal phase support for 10 to 11 weeks.
The main outcome measured was live birth after the first embryo transfer. Secondary outcomes included clinical pregnancy rates, rates of singleton or twin pregnancies, ectopic pregnancy, pregnancy loss, and other birth and maternal complications.
The final analysis included 838 women, with 419 in each group. While 5.3% of women in the frozen embryo transfer group did not undergo the procedure within a year after randomization, only 0.5% of women in the fresh embryo transfer group had the same outcome. The groups had similar baseline characteristics and ovarian stimulation results.
The live birth rate was 32% in the frozen embryo transfer group and 40% in the fresh embryo transfer group, a difference of 8.6%. Other outcomes showed that twin live births occurred in 5% of the frozen group compared to 9% of the fresh group. Clinical pregnancy rates were 39% for the frozen group and 47% for the fresh group, while pregnancy loss occurred in 31% of the frozen group and 23% of the fresh group. The cumulative live birth rate was 44% in the frozen group and 51% in the fresh group.
Overall, the study found that fresh embryo transfer might be a more effective option for women with a low prognosis for IVF, leading to higher live birth rates compared to frozen embryos. The researchers recommend further studies to explore strategies such as accumulating embryos through back-to-back IVF cycles.
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- Infertility: Facts, Diagnosis, and Risks
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