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Assisted Reproduction

Study: Two Embryos Is The Magic Number For IVF Transfers

According to a new report in the medical journal, The Lancet, no more than two embryos should be implanted during an IVF cycle. The decision between whether to transfer one or two should be decided based upon prognostic indicators, such as age, according to this new report. Notably, the transfer of three embryos resulted in a live birth rate lower than if two embryos were implanted coupled with an increased risk of adverse perinatal outcomes:

Transferring three or more embryos during in vitro fertilization (IVF) should be avoided in all cases, and the choice of one versus two should be made based on risk factors such as age, a study has found.

When two embryos were transferred, the odds ratios of live birth were higher in women 40 years or older than in younger women, compared with transferring only one embryo (3.12, 95% CI: 2.56 to 3.77 for older women, versus 2.33, 95% CI 2.20 to 2.46 for younger women; P=0.0006 for the interaction) noted Scott M. Nelson, BSc, MBChB, PhD, MRCOG from the University of Glasgow in the United Kingdom, and colleagues.

The absolute difference in risk of live birth was smaller for women 40 and older (0.090, 95% CI 0.080 to 0.099) than for younger women (0.156, 95% CI 0.148 to 0.163; P< 0.0001), they wrote online in The Lancet. Action Points Although authorities recommend limiting the number of embryos transferred, "40% of treatment cycles in the U.S. and 21% in Europe involve transfer of at least three embryos, and 20–30% of pregnancies resulting from in­ vitro fertilization are twin or higher-­order multiple gestations," the authors noted, adding that most studies on the issue involve women under 40. To learn more about the differences in outcomes among younger and older women undergoing IVF, the researchers accessed records of the U.K. Human Fertilization and Embryology Authority. The authority is required by law to collect baseline and outcome information on all licensed fertility treatment cycles in the country. They focused on treatments registered between January 2003 and December 2007. Live births were defined as at least one baby born alive after 24 weeks' gestation who survived for at least one month. Outcomes included any live birth versus multiple live births. They also included preterm births (less than 37 weeks versus 37 or more), severe preterm births (less than 33 weeks), and low birthweight babies (less than 2.5 kg). During the study period, there were 124,148 IVF cycles resulting in 33,514 live births. In 73% of the cycles, at least four embryos were available, although in most of those cases (83%) two were transferred. In both older and younger women, the proportion of cycles ending in live birth was greater after the transfer of two embryos than when only one was transferred. In women younger than 40 years, transfer of three embryos resulted in a live birth rate that was lower than that seen for two embryos; for older women, the live birth rate was the same whether two or three embryos were transferred. In general, transfer of three embryos was associated with an increased risk of adverse perinatal outcomes. Among the 32,732 cycles with complete data that resulted in at least one live birth, the multiple birth rate was 24.3 per 100 live births (95% CI 23.9 to 24.8). About 1 in 5 cycles with live births were preterm, and a quarter were low birthweight. Odds ratios for those outcomes were raised for multiple versus singleton births. They remained similar when twins were compared to singletons. The absolute differences in risk of live birth after transfer of two or more embryos compared with only one were smaller in the older women. Younger women would need fewer two-embryo cycles to gain an extra live birth. However, an increase also was seen in all of the adverse outcomes, indicating the younger women are also at higher risk for these complications. Limitations include incomplete data for 12% of the cycles. The use of treatment cycles instead of actual patients to maintain privacy meant that the investigators were unable to account for possible clustering and they could examine cumulative outcomes such as live births in women who had two consecutive cycles. And, unlike in randomized, controlled trials, the researchers could not tell if the transfer of only one embryo was elective or related to available embryos. "Our results support guidance to restrict the number of transferred embryos to one or two, but suggest greater freedom can be afforded to clinicians and patients to make decisions about whether to transfer one or two embryos on the basis of prognostic indicators, such as maternal age and the number of embryos successfully fertilized," said the authors. "The transfer of three or more embryos at any age should be avoided." In a comment in the same issue of the journal, Liv Romundstad, MD, from St. Olav's University Hospital in Trondheim, Norway, notes that the increases with multiple births and preterm deliveries seen in assisted contraception adds a major financial burden to health care systems. However, that has to be weighed against the possible need for more cycles if fewer embryos are transferred. "This important paper provides strong arguments in favor of restricting the transfer of embryos to a maximum of two per cycle, irrespective of maternal age," wrote Romundstad.

Note: The Lancet site is down for maintentance so I have quoted the summary from MedPage Today.


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