Good IVF success rates after single embryo transfers
By Dr. Kirsty Horsey
Transferring one IVF embryo, followed by a second, frozen-thawed
embryo if the first fails to implant, is almost as likely to result
in a pregnancy as transferring two at a time - in women under 35,
Swedish researchers report. Team leader Christina Bergh, based at
the Sahlgrenska University Hospital, says that the benefit of the
approach is 'the dramatic decrease in multiple birth rate with no
substantial reduction in the overall live birth rate'. The findings
are published in the latest issue of the New England Journal of
Medicine.
In recognition of the health risks associated with multiple births,
for both women and children, several countries have legislation or
guidelines that limit the number of embryos that can be transferred
to the womb following IVF treatment. In 1993, Swedish IVF doctors
started to reduce the number of embryos transferred into a woman
from three to two. For the latest study, 661 women under the age of
36 with at least two good quality embryos were randomly assigned
into two groups. In the first group, the women underwent a transfer
of two fresh embryos, while in the second, just one embryo was
transferred. Doctors then transferred a second, frozen-thawed
embryo, if the first did not result in a pregnancy.
The results showed that the single embryo transfer method resulted
in a similar live birth rate to the two embryo group. In the two
fresh embryo group, 142 of 331 (42.9 per cent) women had
pregnancies resulting in at least one live birth, whereas in the
second group, 128 of 330 women (38.8 per cent) had one live birth.
27 per cent of the second group became pregnant after a single
embryo transfer, while the rest had to have a second embryo
transferred.
'IVF has come a long way since the early days when you would put in
four embryos and have a 15 per cent success rate', said Owen K
Davies, author of an editorial that accompanies the new study. 'Now
that each embryo has a better chance of implanting than they used
to, we have the luxury of worrying about multiple births', he
added. However, he also stressed that the women taking part in the
study were likely to become pregnant through IVF - their average
age was 31, it was only their first or second attempt at IVF, and
each had at least two viable embryos. In the US, said Davies,
unlike Sweden and other European countries, 'patients go to IVF as
the last resort', so their average age tends to be much older. He
also pointed out that only 50-75 per cent of embryos survive the
freeze-thawing process, so that 17 per cent of the women in the
study did not have the option of a second embryo transfer.
US infertility specialist Eric Surrey says that it is increasingly
clear that for patients with a good chance of conception, single
embryo transfer may be preferable to multiple transfers. However,
he points out that in the US, 'insurance almost never pays for in
vitro fertilisation, so maximising the chances of pregnancy the
first time around is a big concern'. He also says that couples who
don't have children often see twins as 'a desirable outcome',
seeing it as 'two for the price of one'. Davies says that the vast
majority of twins do 'just fine', but the risk is considerably
higher than for single birth pregnancies. 'Having babies one at a
time is safest', he said.
Source: www.BioNews.org.uk