In vitro fertilization with single euploid blastocyst transfer a randomized controlled trial

The Blastocyst Euploid Selective Transfer (BEST) Trial demonstrated that single euploid blastocyst transfer results in ongoing pregnancy rates that are equivalent to transferring two untested blastocysts, while dramatically reducing the risk of multiple gestations.

Eric J. Forman, M.D., Kathleen H. Hong, M.D., Kathleen M. Ferry, Xin Tao, Deanne Taylor, Ph.D., Brynn Levy, Ph.D., Nathan R. Treff, Ph.D., Richard T. Scott, Jr., M.D.

Volume 100, Issue 1, Pages 100-107.e1, July 2013


To determine whether performing comprehensive chromosome screening (CCS) and transferring a single euploid blastocyst can result in an ongoing pregnancy rate that is equivalent to transferring two untested blastocysts while reducing the risk of multiple gestation.

Randomized, noninferiority trial.

Academic center for reproductive medicine.

Infertile couples (n = 205) with a female partner less than 43 years old having a serum anti-Müllerian hormone level ≥1.2 ng/mL and day 3 FSH

Randomization occurred when at least two blastocysts were suitable for trophectoderm biopsy. The study group (n = 89) had all viable blastocysts biopsied for real-time, polymerase chain reaction–based CCS and single euploid blastocyst transfer. The control group (n = 86) had their two best-quality, untested blastocysts transferred.

Main Outcome Measure(s):
The ongoing pregnancy rate to ≥24 weeks (primary outcome) and the multiple gestation rate.

The ongoing pregnancy rate per randomized patient after the first ET was similar between groups (60.7% after single euploid blastocyst transfer vs. 65.1% after untested two-blastocyst transfer; relative risk [RR], 0.9; 95% confidence interval [CI], 0.7–1.2). A difference of greater than 20% in favor of two-blastocyst transfer was excluded. The risk of multiple gestation was reduced after single euploid blastocyst transfer (53.4% to 0%), and patients were nearly twice as likely to have an ongoing singleton pregnancy (60.7% vs. 33.7%; RR, 1.8; 95% CI, 1.3–2.5).

In women ≤42 years old, transferring a single euploid blastocyst results in ongoing pregnancy rates that are the same as transferring two untested blastocysts while dramatically reducing the risk of twins.

Clinical Trial Registration Number:

  • J.W.

    I’m awaiting my CCS results now. I’m wondering why lean anovulatory PCOS women were excluded from the best trial. This describes me and I’ve just produced 23 fertilized eggs, so it must not be because of poor prognosis, right?

  • DPD

    Congrats! I’m a 32-year-old patient at the center that conducted this trial. We were not part of the trial, but we chose eSET with CCS and had wonderful success – along with 4 other genetically normal blastocysts vitrified for later use. Thank you to all the doctors who made this possible!

  • Eric Forman

    Thank you for your kind comments. We see comprehensive chromosome screening (CCS) as a pathway to bring the benefits of single blastocyst transfer to the vast majority of infertility patients, resulting in similar delivery rates but improved obstetrical and neonatal outcomes. Without changing the way embryos are selected, DET will always have a higher delivery rate than SET and patients may feel they are compromising their chances for a successful cycle. Though others have criticized this approach for couples who want multiple children, most patients in this study had other euploid blastocysts vitrified individually. Several have already come back for a second SET.

    This approach has been very well received by patients. When we initiated the study we were concerned patients would not want to be randomized to SET. In fact, more patients actually wanted CCS performed with SET and some patients were upset to be randomized to the DET group without CCS. In clinical practice this approach is frequently being utilitzed by our patients, regardless of their age.

    • Micah Hill

      That is very encouraging to hear how well it is being received!

  • Micah Hill

    Congratulations Eric and others on another remarkable study! I appreciate the extensive steps your group has taken to validate this technology and now rigorously test its clinical application. I agree that a cost analysis would very likely show a substantial cost benefit to screening embryos and performing SET, due to the marked reduction in twins. My question is how do you see this practically deploying into clinical use outside of the research setting? While it may be of cost benefit on the overall level, do you think individual patients are likely to pay extra money to utilize this? Have you had a positive patient response to this data outside of the research setting?

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