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Infertility Research Shows Frozen Embryo Transfers Yield Higher Pregnancy Rates

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January 22, 2013

Without infertility clinical trials, the field of reproductive medicine would not be what it is today. Current research aims to transfer fewer embryos while yielding high implantation and pregnancy rates, and fertility doctors are relying more and more on the use of Frozen Embryo Transfer (FET) and Preimplantation Genetic Diagnosis (PGD) to make this possible.

Bruce Shapiro, M.D., of The Fertility Center of Las Vegas, is a leader in some of the research responsible for the recent buzz about Frozen Embryo Transfers for increased implantation and pregnancy rates. “In a [traditional] IVF cycle, fertility medications create suboptimal conditions for embryo implantation to occur,” he says. In two clinical trials, Dr. Shapiro discovered that the implantation and pregnancy rate was two-thirds higher for those who had undergone a Frozen Embryo Transfer in a subsequent cycle, versus transferring embryos during the same cycle in which fertility drugs were used.

In order to maximize a fertility patient’s odds for developing healthy, chromosomally sound embryos, fertility doctors aim to stimulate and retrieve a high number of eggs. While fertility drugs allow for greater ovarian stimulation than a natural (not medicated) IVF cycle, Dr. Shapiro explains that the effects of increased estrogen and progesterone actually diminish the endometrial lining. This produces an effect called embryo-endometrial asynchrony, or unfavorable conditions for the embryo to implant.

“In a frozen cycle, we thaw the embryos at just the right time to make sure the timing is perfect,” says Shapiro. Frozen embryo transfers allow the uterine lining to return to its natural receptivity and reduce the odds of failed implantation or miscarriage.

Dr. Shapiro states most patients at his facility are encouraged to do “thaw” transfers versus fresh transfers, particularly if they have experienced prior failed IVF cycles. “We always worry about failures, but it is time to switch gears and find out why we have had a failure.” He says embryos have been blamed as the cause of failed cycles, rather than considering the receptivity of the endometrial lining.

“As time goes on, more physicians will put back thawed embryos,” he says, confidently. The concept of frozen transfers is not new; in fact, frozen transfer is common with PGD or after a fresh transfer has failed to produce a pregnancy. However, the scientific evidence of increased implantation rates may have sparked the movement toward FET as the standard of care.


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