Towards a new technique for pre-implantation genetic embryo screening in IVF, pilot phase

The success rate of in vitro fertilization (IVF) procedures is determined by
many variables. One important variable is the selection of a high quality
embryo for transfer into the uterus. It is however, difficult to assess embryo
quality. Currently the only routinely used parameters are morphologic features
assessed by microscopy. A high percentage of human embryos contain aneuploid
cells which is likely to affect pregnancy rates. Pre-implantation genetic
screening (PGS) can detect such an aneuploidy by using fluorescent in situ
hybridization (FISH) on a single cell obtained from an embryo. Hence, PGS
allows for screening and selection of IVF embryos based on chromosomal
integrity. It is assumed that such a selection of the *best* embryo for
transfer would lead to an increase in ongoing pregnancy rate and a decrease in
the number of miscarriages. Randomized controlled trials could however not
detect an inceased pregnancy outcome in the biopsy PGS group. Hence the
benefits of PGS are not yet established. The PGS procedure is thought to be
safe since biopsied embryos show normal outgrowth to blastocysts. However,
subsequent outgrowth to later developmental stages has not been analysed
independently of embryo selection. It is possible that several steps in the
biopsy procedure cause small traumas to the embryo that may result in a
decreased implantation potential even though its outgrowth to a blastocyst is
not affected. Such negative effects may counterbalance the positive effect of
PGS selection and hence it seems important to explore less traumatic nuclear
extraction procedures to be used in PGS.

The objective of this study is to evaluate a new and less invasive method of
PGS. The new PGS technique will analyse a nucleus of a blastomere that was
obtained by nuclear extraction rather than by biopsy of a whole blastomere.

The study will consist of a pilot project to investigate the methodological
aspects of the enucleation procedure, and if successful, permission for a
subsequent prospective randomized trial (RCT) with IVF patients, using
enucleation-PGS will be requested from the CCMO. The pilot study will have to
provide answers on how to perform the enucleation and a validation of the FISH
procedure as well as whether outgrowth of enucleated embryos to blastocysts is
normal.

For enucleation in spare-embryos, a sharp micro-pipette is used to isolate the
nucleus and the remaining cytoplasm from a single blastomere and in biopsy-PGS
a whole blastomere is isolated using standard biopsy techniques. The nuclei are
used for FISH analysis with 10 chromosomal probes and the remainder of the
embryo is used in a comparative outgrowth test with control embryos.

Biopsy-PGS does not result in an increased number of abnormal offspring. Biopsy
of a blastomere does not lead to differences in in-vitro development but is
suspected to reduce the developmental potential of embryos. We expect the
enucleation procedure to be saver and less traumatic compared to a conventional
biopsy procedure. This study will use spare embryo's and the donating patients
will thus not receive any burden or risks.