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NEW YORK (Reuters Health) - The transfer of a single embryo
into the uterus decreases the number of twin pregnancies
without adversely affecting pregnancy outcomes, according to a
report in the current issue of Fertility and Sterility.
Recent efforts have focused on transferring fewer embryos
as a means of reducing the rising rate of twin pregnancies, the
authors explain. Several studies have shown similar pregnancy
outcomes, 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, Boston, 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.
IVF cycle characteristics did not differ between the
single- and double-embryo transfer groups, the report
indicates.
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, the authors report. 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.
More double-embryo transfer cycles (51 percent) than
single-embryo transfer cycles (3.1 percent) resulted in twin
pregnancies, the researchers note.
Moreover, there was no difference 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.
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, the researchers explain.
The most important factor in the decision to proceed with
elective single-embryo transfer, they add, may be for women
with a "favorable reproductive profile."
SOURCE: Fertility and Sterility, June 2008.
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