Two Methods of Implanting Embryos Yield Similar Success Rates

Yale School of Medicine
Monday, 30 October 2000

Finding Contradicts National Database

Contrary to official figures, two methods of fertilization - implanting the embryo in the uterus or in the Fallopian tube - yield comparable success rates, a study by a Yale researcher has concluded.

The study by Steven Palter, M.D., assistant professor and clinic chief of reproductive medicine in the Department of Obstetrics and Gynecology at Yale School of Medicine, contradicts statistics published by the Centers for Disease Control and the Society for Assisted Reproductive Technology. Those statistics show that implantation in the Fallopian tube, which is more risky and more costly, has a higher success rate for fertilization.

"Our study shows that there is no difference in implantation and pregnancy rates among women undergoing zygote intrafallopian transfer (ZIFT) and intrauterine embryo transfer (ET)," said Palter, who presented his findings at a meeting of the American Society for Reproductive Medicine in San Diego, Calif. "When you combine the expense and scheduling difficulties associated with ZIFT, this technique cannot be recommended for routine use."

Both the national database and Palter's study showed that the ZIFT procedure leads to increased risk of an ectopic pregnancy in which the fertilized egg implants outside the womb, most often in the Fallopian tube. As the embryo develops the tube ruptures or other complications arise.

The national database was mandated by Congress in 1992. The law requires that pregnancy success rates for assisted reproductive technology (ART) procedures carried out in fertility clinics be published. The statistics have consistently shown that the transfer of embryos to the Fallopian tube had a significantly higher success rate.

Palter said he and his co-author, Antonia Habana, at the time a postdoctorate research fellow, analyzed 24 studies, which included several randomized controlled trials. The researchers reviewed 548 cycles, which is the number of in vitro fertilization attempts; 514 egg retrievals, and 388 transfers into the uterus or Fallopian tube. Each case was comparable in terms of mean age, the cause of the infertility, the protocol used, and the number of transfers. They found the implantation rate and pregnancy rates were not significantly different.

Palter said an explanation for the contradictory findings is that the fertility clinics, once they were required to publish their rates of implantation and pregnancy, began accepting women patients who were most likely to have a successful procedure.

"The original intention of the database was not to serve as a basis for direct comparisons between procedures or clinics, but merely for each clinic to be accountable and publish its success rate," he said. "Unfortunately, since it was mandated by Congress to be published and it is available on the Internet, many patients and physicians directly access the report and are using it to choose their practitioner or procedures."

Palter said his study demonstrates that there is a high likelihood of bias in the database in how patients are selected for different procedures, "and it cautions us from overinterpreting the results beyond what they were originally intended for."

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