Two-embryo transfer is as
effective as three in new IVF procedure
BY RUTHANN RICHTER
Women who have undergone a
new in vitro fertilization (IVF) procedure known as
blastocyst transfer are just as likely to get pregnant if
doctors transfer two embryos into the womb, as opposed to
three, according to a new study by Stanford researchers.
The study indicates that the new IVF approach can
virtually eliminate the chance of triplets which can
be risky to the pregnancy while maintaining, or
possibly even increasing, a woman's chances of getting
pregnant, said Amin Milki, MD, associate professor of
gynecology and obstetrics and the lead author on the
study.
"There are two major
gambles with IVF," said Milki, medical director of
Stanford's IVF program. "The first gamble is getting
pregnant versus not getting pregnant. Once you achieve a
pregnancy, the woman's second worry begins how
pregnant am I? This technique won't decrease her odds of
conceiving and at the same time avoids her risk of having
triplets."
The study involved 55
Stanford patients who chose to undergo blastocyst
transfer in 1998, when Stanford first began offering the
procedure. During the procedure, the embryo is bathed in
a culture of nutrients for five days until it reaches a
developmental landmark known as the blastocyst stage. At
this point, doctors can discern which embryos are most
likely to thrive and make their selection for transfer
into the uterus.
Traditionally, doctors
have performed transfers on day three, often implanting
four or more embryos in the hope that some will do well
and develop into a healthy fetus. However, the
traditional approach sometimes can lead to the conception
of three or more fetuses a number that threatens the
pregnancy and may force women to opt for selective
reduction, the removal of one or more embryos to give the
pregnancy a better chance of success. With the blastocyst
method, doctors can transfer just two or three embryos,
with a good chance of success.
In the study, Stanford
researchers set out to determine whether two embryos
might serve the purpose as well as three, avoiding the
need for selective reduction, Milki said.
Indeed, their results
showed that women who had two embryos transferred had
just as good in fact slightly better chances of
getting pregnant as those who had three embryos
transferred. Of the 29 patients who chose to have a
two-embryo transfer, 62 percent achieved a viable
pregnancy, with all of them passing the first trimester
mark. Among the 24 women who chose a three-embryo
transfer, 58 percent conceived a viable pregnancy, the
researchers reported in the August issue of the journal
Fertility and Sterility.
"We've shown that
with two embryos transferred, we're approximating the
time when we can get a single-embryo transfer, which is
incredible. Nobody previously thought we could transfer
fewer embryos and get a higher pregnancy rate," said
Barry Behr, PhD, assistant professor of gynecology and
obstetrics and a co-author on the report.
Behr, director of the
Stanford's IVF and Assisted Reproductive Technology
Laboratory, developed the special culture used to nurture
the embryos in
the laboratory.
The results suggest there
is no value in transferring more than two embryos and
there is a benefit in that the technique can avoid
high-risk, triplet births. Among the women who had
two-embryo transfers, 39 percent conceived more than one
fetus (all twins). Among those who had a three-embryo
transfer, 79 percent conceived more than one fetus 50
percent twins and the other 29 percent triplets. The
patients who chose to transfer three embryos were
counseled about the risks associated with multiple
gestations. All those who conceived triplets elected to
selectively reduce one embryo to minimize the overall
risk of the pregnancy, Milki said.
Since the researchers
compiled data on the initial 55 patients, Milki said the
Stanford IVF Clinic has performed blastocyst transfer on
an additional 55 women, with similar results.
He noted that success
rates have been high in part because of patient
selection. Blastocyst transfer has been offered to
patients who produce more than three eight-cell embryos
by day three embryos considered likely to do well. But
a separate study by Milki and his colleagues suggests
that patient selection alone isn't the key. Extending
embryo growth for another two days until day five
confers a special advantage, they found. Among women
whose embryos were nurtured for five days before being
transferred, the pregnancy rate was 68 percent, he said.
Among those who chose to have the embryos transferred on
day three before they reached the blastocyst stage
the pregnancy rate was 46 percent, Milki said.
In the latest study, the
research team included Jeffrey Fisch, MD, a fellow in
reproductive endocrinology. The study was funded by
Stanford. SR
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