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 Whereas in women with polycystic ovary syndrome (PCOS), freezing and
thawing embryos before implantation offers a better chance of
pregnancy and birth, in women without this condition thawed embryos
and are no better or worse than fresh embryos, researchers in China
and Vietnam have found.
The findings may encourage doctors to just implant one embryo at a
time, lowering the risks that come when doctors try to implant more,
producing multiple births and their associated complications.
The papers, published in The New England Journal of Medicine, are
"good news for women seeking in-vitro fertilization," said Dr. Lan
Vuong, chief author of the Vietnamese study.
After an earlier study by the Chinese team showed that frozen
embryos were better for women with PCOS, "a lot of people jumped to
the conclusion that we should always do frozen. Some programs around
the country won't do fresh transfers anymore," said Dr. Christos
Coutifaris of the University of Pennsylvania's Perelman School of
Medicine in Philadelphia, who was not connected with the new
research.
"Now these two papers, equally large and done in non-PCOS patients,
show that in terms of live birth, which is what we care about, there
is no difference," he told Reuters Health by phone. "So to apply the
rule to everybody that we should freeze your embryos is probably not
correct."
Dr. Vuong said that in the past, doctors have often implanted more
than one fresh embryo in women because of concerns that a frozen
transfer may not work as well.
The fact that thawed embryos "produce the same pregnancy rate with
less complications should transform the way in-vitro fertilization
is practiced," she told Reuters Health by email. "After the first
fresh embryo transfer, it will be possible to freeze the remaining
embryos and transfer them one by one, if necessary, without reducing
the chance of pregnancy."
Dr. Vuong, of the University of Medicine and Pharmacy at Ho Chi Minh
City, and her colleagues also found that women with high levels of
the female hormone progesterone might be better off receiving a
thawed frozen embryo.
Dr. Coutifaris, who is president of the American Society for
Reproductive Medicine, said a higher progesterone level may indicate
that the development of the embryo and the womb are out of synch,
and using a thawed embryo allows for better timing of the
implantation.
It's one example where "the challenge for us, as practitioners, is
to determine who are the patients who will benefit from a
freeze-only approach," he said.
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In the Chinese study of 2,157 women undergoing their first in-vitro
fertilization cycle, the birth rate was 48.7 percent with thawed
embryos and 50.2 percent with fresh. Doctors typically implanted two
embryos per attempt.
In the Vietnam study of 782 women undergoing their first or second
attempt, the live birth rates after the first transfer were 33.8
percent with frozen and 31.5 percent for fresh. They also implanted,
on average, two at a time.
In both studies, the difference in birth rates between the groups
was so small that it might have been due to chance.
Neither study found a higher risk of neonatal or obstetrical
complications in either group, although frozen embryo transfer
produced a statistically lower risk of over-stimulated ovaries,
which leads to swollen and painful ovaries and is potentially
dangerous.
The rates of the syndrome in the Chinese study were 0.6 percent with
frozen embryos and 2.0 percent with fresh. The senior author was Dr.
Zi-Jiang Chen of Shandong University, who did not respond to emailed
questions.
It was the Chen group that, in 2016, reported that
frozen-then-thawed embryos offered a 7-percentage-point edge when it
came to producing live births among infertile women with polycystic
ovary syndrome: 49 percent versus 42 percent. The improvement came
primarily from a lower rate of pregnancy loss.
"The cost for freezing embryos is about 30 percent more than that
for fresh transfer," said Dr. Vuong. "However, the effectiveness of
the treatment should be considered in decisions about which approach
is more cost-effective. We have done a cost-effectiveness analysis
of the two treatments and found that freezing embryos and subsequent
transfer is not cost-effective over fresh transfer."
SOURCES: http://bit.ly/2m2bPYw and http://bit.ly/2CxHmro The New
England Journal of Medicine, online January 10, 2018.
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