Pregnancy and Multiple Gestation Rates after Transfer of Two Versus Three Blastocysts

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Article Title: "Two-blastocyst transfer has similar pregnancy rates and a decreased multiple gestation rate compared with three-blastocyst transfer"

Authors and Affiliations: Amin A. Milki, Jeffrey D. Fisch, and Barry Behr, Department of Gynecology and Obstetrics, Stanford University School of Medicine.

 

Summarized by Christine M. Schroeder, Ph.D.

In IVF, transfer of more embryos is often associated with a higher chance of pregnancy. However, transferring more embryos also confers an elevated risk of multiple pregnancy. Blastocyst transfer may provide at least a partial solution to this dilemma, because blastocysts have higher implantation rates than day 3 embryos. Because of the higher implantation rates, not as many blastocysts have to be transferred back to the uterus in order to achieve satisfactory pregnancy rates.

The authors of the current study began offering fresh blastocyst transfer routinely to patients who are at risk for multiple gestations in January 1998. All patients were advised to transfer only two blastocysts; however, patients willing to undergo selective reduction were allowed to transfer up to three blastocysts. Despite this fairly conservative policy, the clinic noticed that the proportion of multiple pregnancies at their clinic increased. Due to the fact that there was little information on the issue of multiple pregnancy and the number of blastocysts transferred, the authors decided to compare the two and three day blastocyst transfers.

The study was retrospective, which means that the researchers went back and reviewed the cases of women who had undergone two- and three-blastocyst transfers; in other words, patients were not randomly assigned to type of transfer. Twenty-nine patients had two blastocysts transferred (the 2B group) and 24 had three transferred (the 3B group). Despite the fact that they had not been randomly assigned to treatment, the 2B and 3B groups were similar in age (35.1 years average), the number of previous IVF cycles, the number of oocytes retrieved, the number of embryos on day 3, and the number of blastocysts that ultimately developed. Patients with embryos fertilized conventionally and via ICSI were both included in the study.

Analysis of the results indicated that:

  • The 2B and 3B groups both had implantation rates of 47 percent.
  • Pregnancy was defined as two positive rising hCG tests taken two days apart. The pregnancy rate in the 2B group was 73 percent and in the 3B group, it was 76 percent.
  • Viable pregnancy was defined as visualized fetal cardiac activity at seven and nine weeks gestation. The viable pregnancy rate in the 2B group was 58 percent, and the viable pregnancy rate in the 3B group was 62 percent.
  • The twin pregnancy rate in the 2B group was 39 percent, and the twin pregnancy rate in the 3B group was 50 percent
  • The triplet pregnancy rate in the 2B group was zero percent, and the triplet pregnancy rate in the 3B group was 29 percent

 

Thus, over three fourths of the pregnancies in the 3B group - 79 percent - were multiple gestations, compared to 39 percent in the 2B group. Additionally, none of the multiple gestations in the 2B group were triplet gestations, whereas 36 percent of the 3B group pregnancies were triplet gestations.

Thus, two blastocyst transfers sharply reduce the risk of multiple gestation, with no compromise in overall pregnancy rate. Based on these results, the researchers strongly recommend that patients be encouraged to transfer only two blastocysts.

 

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