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IVF Pregnancy and Implantation Rates Higher in North America, Says Study

by Leigh Ann Woodruff, April 19, 2012

Are North American IVF labs better at in vitro fertilization? A new study, published online in Fertility and Sterility reports that cumulative ongoing pregnancy rates and live birth rates after in vitro fertilization (IVF) were considerably higher in North America than in Europe.

"It's the first time that there has been a group of patients worldwide cycling with the same medications, and the doctors and the centers and the patients were blinded, and all the protocols were the same, but the outcomes were very different," says study author Robert Boostanfar, M.D., a fertility doctor with HRC Fertility in Encino, CA. "When you control for number of embryos transferred, and you look at implantation rates, then you can find that we're doing a slightly better job at North American centers."

The Study

Dr. Boostanfar's retrospective study was part of the Engage trial, a randomized, double-blind, noninferiority study in which controlled ovarian stimulation with corifollitropin alpha was compared with injections of recombinant follicle-stimulating hormone (rFSH) in an otherwise standard gonadotrophin release hormone antagonist protocol. The study had 804 North American patients with 14 North American fertility clinics and 702 European patients with 20 fertility clinics in Europe.

"I had asked if we could do a subset analysis because this was a unique study," Dr. Boostanfar says. "It was the same patient population, it was prospective, randomized, controlled and blinded. It was an optimal group of fertility patients that had strict inclusion and exclusion criteria. All the centers had to follow the same inclusion and exclusion criteria."

The women participating had to be between 18 and 36 years of age, with a body weight between132 and 198 pounds, regular menstrual cycles of 24 to 35 days, and a partner with ejaculatory sperm. "These were basic, good fertility patients, with good follicle counts and good FSH," Dr. Boostanfar says.

The researchers found that the live birth rate in North America was 39.2 percent in both treatment groups compared with 31.5 percent in Europe after corifollitropin alpha (a single injection stimulating egg production for seven days) and and 28.8 percent after recombinant FSH (daily injection) treatment. When considering the number of embryos transferred, the live birth rate per embryo transfer was still higher in North American than Europe — 42.7 percent vs. 36.8 percent with corifollitropin alpha and 41.6 percent vs. 30.9 percent with recombinant FSH.

"The big criticism that the Europeans have with the U.S. doctors is that we put in too many embryos, and our pregnancy rates are higher because of that," says Dr. Boostanfar. "And that, to some degree, is true. But, what we did find was that the implantation rates were better in the study. And that's a big difference because you can now attribute higher pregnancy rates to not just more embryos, but better embryo selection, maybe better embryo transfer technique, maybe better laboratory technique."

Implantation rate is the number of sacs per embryo transferred. Pregnancy rate is the number of sacs per transfer. For example, if you transfer one embryo and get one sac, that's a 100 percent implantation rate. If you transfer two embryos and get one sac, that's a 50 percent implantation rate and a 100 percent pregnancy rate.

The researchers also found that North American fertility doctors tended to obtain more eggs and embryos per cycle. "Maybe we're more aggressive about retrieval or better at retrieval," Dr. Boostanfar says. "Maybe American patients responded better to the drug."

The Takeaway

Transferring more than one embryo is part of the reason there are higher pregnancy and live birth rates with IVF in North America, but it's not the whole story. Dr. Boostanfar recommends that patients in all countries discuss with each fertility clinic what procedures and protocols they use in the laboratory to try to select the best embryos and the best transfer technique for embryos.

"For years, you look at SART rates and you look at rates in another country in Europe, and they say, 'Well, the Americans are putting in 2.1 embryos per transfer, and we're putting in 1.1 embryos per transfer. So of course you are going to have a higher clinical pregnancy rate, ongoing birth rate, live birth rate, etc.' Now, we can take a group of patients that are essentially the same in both continents — they have the same protocol, everything was the same — and we're able to extract why is there a difference," Dr. Boostanfar says. “If we have a higher implantation rate, we are either creating embryos, selecting embryos or transferring these embryos in a more effective way.

"I think it's a combination of all three."


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