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Infertility & Reproduction Health Center

IVF Technique Could Reduce Multiple Births

Researchers Report Good Outcomes With Single-Embryo Transfer
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Dec. 1, 2004 -- Couples struggling with infertility often choose in vitro fertilization to achieve pregnancy. Twins are common with in vitro fertilization (IVF). But new research shows that the risk of multiple births can be decreased without lessening the chances of having a baby.

During in vitro fertilization, the egg is fertilized in a lab and implanted into the womb. Traditionally, more embryos are put into the womb during IVF to increase the chances of delivering a baby.

According to a new Swedish study, putting one embryo into the womb during IVF significantly reduces the risks associated with twin births. And the researchers found that this led to similar birth rates as that seen when two embryos were put in simultaneously.

"Couples often don't think of twin births as being that much more risky than a single birth, but it is clear that they are," researcher Christina Bergh, MD, PhD, tells WebMD. "Studies have shown that twins have a five- to 10-times higher risk for whatever poor outcome you measure, including death and malformations."

According to the researchers, the most important factor in determining the number of births is the number of embryos transferred into the womb during IVF procedures.

The researchers tested putting one vs. two embryos into the womb to see if there was a difference in birth rates.

For women that received a single embryo, a second embryo was put into the womb only if the first embryo failed to implant.

This method resulted in a birth rate that was only slightly lower than when two embryos were put in simultaneously -- a 39% birth rate for single-embryo transfer vs. a 43% birth rate for double-embryo transfer.

However, the single-embryo transfer group had significantly fewer multiple births. The twin birth rate among the double-embryo transfer group was 33%, compared with 0.8% for the single-embryo group.

The study is published in the Dec. 2 issue of the New England Journal of Medicine.

Bergh says that single-embryo transfer should be considered for all women undergoing IVF who have a good chance of achieving a pregnancy. Women under 35 with good-quality embryos who have failed no more than one previous IVF attempt are generally considered to be the best candidates.

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