Articles
Register for Reduce Multiple Pregnancies in PGD Cycles without Adversely Affecting Pregnancy Rates
ESHRE XXV, Amsterdam
June 29 - July 1, 2009
Research shows it is possible to freeze embryos and reduce multiple
pregnancies in PGD cycles without adversely affecting pregnancy rates
Transferring just one embryo at a time to a woman’s womb after embryos have
undergone preimplantation genetic diagnosis (PGD) and freezing at the blastocyst
stage has become a real option after researchers achieved pregnancy rates that
were as good as those for blastocysts that had not had a cell removed for PGD
before freezing. Their results mean that it will be possible to reduce the
number of multiple pregnancies after PGD and the consequent complications
associated with these pregnancies.
The research was presented at the 25th annual meeting of the European Society of
Human Reproduction and Embryology in Amsterdam and published online in Europe’s
leading reproductive medicine journal, Human Reproduction, simultaneously.
Dr Yacoub Khalaf, director of the assisted conception unit at Guy’s and St
Thomas’ Hospital, London (UK), told the conference: “To the best of our
knowledge, our study is the first to provide reassurance that a strategy of
elective single embryo transfer in good prognosis patients seeking PGD, backed
by an efficient PGD cryopreservation service, can result in pregnancy rates that
are comparable to those for non-biopsied embryos that are frozen as part of
conventional fertility treatment. These results should empower fertility centres
to include PGD cycles for inherited genetic disorders in their efforts to reduce
the multiple pregnancy rates after various forms of assisted conception
treatment. Given the increasing number of PGD cycles performed each year, the
advantage of widespread application of this policy would be considerable.”
Until now, fertility specialists have not applied a single embryo transfer
policy to PGD for inherited genetic disorders because of concerns about how well
biopsied embryos survive after freezing and thawing. “It was thought that the
effect of the biopsy might reduce the embryos’ tolerance to freezing. This
concern was not based on any scientific evidence, only on observations of low
survival rates of biopsied frozen embryos,” said Dr Khalaf.
From January 2006 to July 2008 Dr Khalaf and his colleagues offered single
embryo transfer together with freezing of surplus blastocysts to couples seeking
PGD for single inherited genetic disorders such as cystic fibrosis. All the
embryos were biopsied for the purposes of PGD on the third day after
fertilisation, which is the time that they start to divide. Healthy embryos were
cultured in the laboratory for a further two to three days to check that they
were capable of reaching the next appropriate stage of development – the
blastocyst stage. At this point, 32 couples who had two or more embryos that had
successfully reached the blastocyst stage were offered the option of having one
transferred to the womb and the rest frozen.
The researchers compared the pregnancy outcomes from a subsequent 32
frozen-thawed PGD cycles in these couples with the pregnancy outcomes from a
control group of couples where 191 cycles of conventional IVF/ICSI were carried
out using embryos that were frozen and thawed before implantation, but not
biopsied at any stage.
They found that the blastocyst survival rate after thawing was similar between
the PGD and IVF/ICSI groups (87% versus 88% respectively). There was no
significant difference in the implantation and clinical pregnancy rates (35%
versus 29% and 34% versus 36% respectively). The overall ongoing pregnancy rate
for all frozen cycles (PGD and IVF/ICSI) was 34%, which compares favourably with
the UK national average for frozen cycles (currently 18% live birth rate per
thaw).
When the same period was compared with the period before the single embryo
transfer policy was introduced for PGD couples, the multiple pregnancy rate in
the cycles of fresh PGD dropped from 36% to 10% with no reduction in pregnancy
rates.
Dr Khalaf said: “This research suggests that responsible clinical decisions do
not have to come at the expense of reducing effectiveness of treatment. You can
be responsible and maintain the chances of success for your patients by good
clinical judgment and using the appropriate techniques.
“For patients, this provides reassurance that a couple’s chance of having a
healthy child is not reduced by replacing only one blastocyst and freezing the
surplus ones. Those frozen blastocysts do have a very good chance of leading to
a healthy pregnancy too, and, therefore, patients will not feel pressurised to
have more than one embryo replaced (with the increased risk of multiple
pregnancies) in order to make use of their biopsied, unaffected embryos for
which, otherwise, they might have little use. Now, these frozen blastocysts
offer them the chance of an additional healthy pregnancy without having to go
through the whole treatment cycle again.”
The first author of the paper in Human Reproduction, Dr Tarek El-Toukhy, a
consultant in reproductive medicine and PGD at the assisted conception unit at
Guy’s and St Thomas’ Hospital, said: “This study represents a continuation of
our efforts to advance IVF and PGD safety through single blastocyst transfer and
embryo freezing.”
Full paper published in Human Reproduction. doi:10.1093/humrep/dep172
