July 25, 2008

Report Finds Single-Embryo Transfer Offers Best Pregnancy Results

A new report on fertility methods suggests that the transfer of a single embryo into the uterus decreases the number of twin pregnancies without adversely affecting pregnancy outcomes.

The authors stated that recent efforts have focused on transferring fewer embryos as a means of reducing the rising rate of twin pregnancies. Similar pregnancy outcomes have been seen in other studies, but a lower rate of twin births, after the transfer of a single embryo in women under the age of 37 years.

Dr. Aaron K. Styer and colleagues from Massachusetts General Hospital in Boston performed the research.

The researchers compared the pregnancy outcomes of 52 women who underwent in vitro fertilization (IVF) with a single-embryo transfer versus 187 women who underwent a double-embryo transfer. All of the subjects were 37 years old or younger.

The report indicates that IVF cycle characteristics did not differ between the single- and double-embryo transfer groups.

The research showed that single-embryo and double-embryo cycles also did not differ in the rates of pregnancy - 61 percent versus 63.4 percent - or in rates of pregnancy loss - 20 percent versus 18.6 percent, retrospectively. However the rate of implantation was significantly greater for single-embryo transfer cycles (70.5 percent) than for double-embryo cycles (47.8 percent).

No single-embryo transfer cycles resulted in ectopic pregnancies. An ectopic pregnancy occurs when the embryo does not implant on the lining of the uterus, but somewhere else, usually the fallopian tubes. If not detected early, the consequences can be serious. In contrast, 2 percent of double-embryo transfer cycles did result in ectopic pregnancies, despite the lack of risk factors.

The researchers found that more double-embryo transfer cycles (51 percent) than single-embryo transfer cycles (3.1 percent) resulted in twin pregnancies.

Also, no differences were found in live-birth rates between the single-embryo-transfer group (53.8 percent) and the double-embryo transfer group (54.4 percent).

"This study provides further evidence that elective (single-embryo) transfer is not only a feasible but a realistic option in the young patient who has a favorable reproductive profile and several good-quality embryos available for transfer and cryopreservation," the authors conclude.

The research explained that candidates for the single-embryo transfer may include patients who don't want to risk multiple pregnancies or who have a preexisting medical condition for which a multiple pregnancy would not be safe.

They added that the most important factor in the decision to proceed with elective single-embryo transfer might be for women with a "favorable reproductive profile."

The report was published in the current issue of Fertility and Sterility.


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