A recent study published in the BMJ has revealed that the cumulative live birth rates for blastocyst stage embryo transfers are comparable to those of cleavage stage embryo transfers among women who have four or more embryos available during in vitro fertilization (IVF) treatment.
Since the introduction of assisted reproductive technology in 1978, more than 10 million successful births have been documented. A recent public opinion poll reflects a growing consensus in favor of expanding access to IVF, with 67% of respondents aged 18 and older advocating for mandatory IVF coverage in health insurance plans. Among those, 34% expressed strong support, while 32% were generally supportive, leaving only 7% opposed to the initiative.
Traditionally, IVF or intracytoplasmic sperm injection (ICSI) involved transferring embryos on day 3 post-oocyte retrieval. However, advancements in in vitro culture techniques have shifted this practice to days 5 or 6. This change was predicated on the belief that only viable embryos can develop to the blastocyst stage, leading to the assumption that blastocyst transfers would enhance live birth rates. Nonetheless, the relative success of blastocyst versus cleavage stage transfers regarding live births remained uncertain.
To investigate this question, researchers conducted a randomized controlled trial involving women aged 18 to 43 who were undergoing their first, second, or third IVF or ICSI cycle, with a minimum of four embryos available for transfer. Women who had undergone preimplantation genetic testing or those using frozen-thawed or donor oocytes were excluded from the study.
Participants were randomized in a 1:1 ratio based on age two days post-oocyte retrieval. Ovarian stimulation protocols utilized either gonadotrophin-releasing hormone agonists or antagonists, with local investigators determining the appropriateness of ICSI use. In the study, embryo transfers were conducted on day 5 for the blastocyst group and on day 3 for the cleavage group. Notably, women aged 38 or older were permitted to undergo double embryo transfers.
The primary outcome measured was the cumulative live birth rate within 12 months post-randomization. Secondary outcomes included pregnancy rates, rates of pregnancy loss, live birth rates following fresh embryo transfers, canceled transfers, the number of embryos required for live birth, rates of multiple pregnancies, and obstetric and perinatal outcomes.
Of the 603 women assigned to the blastocyst group, 10 withdrew, while 599 women in the cleavage group saw 43 withdrawals. Importantly, there were no canceled fresh embryo transfers due to unsuitable embryo development.
The intention-to-treat analysis indicated a cumulative live birth rate of 58.9% for the blastocyst group, compared to 58.4% for the cleavage group. This translates to a mere 0.4% difference and a risk ratio of 1.01, underscoring that live birth rates are statistically similar between the two groups.
For secondary outcomes, the cumulative pregnancy loss rate was 16.3% for the blastocyst group and 24.2% for the cleavage group, yielding a risk ratio of 0.68. The live birth rates after fresh embryo transfer were recorded at 37% for the blastocyst group and 29.5% for the cleavage group, with the average number of embryo transfers needed for live birth being 1.55 and 1.82, respectively.
These findings suggest that cumulative live birth rates for both blastocyst and cleavage stage embryo transfers are similar in women with a minimum of four embryos. The researchers recommend further investigation into secondary outcomes to address potential safety concerns.
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