Genetic Diagnosis (PGD)
genetics (PGD) is a state of the art procedure that
is used to allows the genetic analysis of an embryo
prior to transfer, thus prior to implantation and pregnancy.
PGD must be done in conjunction with IVF.
for PGD includes patients with history of genetic linked
disorders, advanced maternal age, recurrent miscarriages,
unexplained infertility, unsuccessful IVF cycles, or
male factor infertility. The most common indication
is a chromosome abnormality in one or both partners.
couples are at risk for transmitting genetic diseases
to their children. These genetic abnormalities may occur
in the sperm or egg and include aneuploidy (which are
eggs or sperm with an abnormal number of chromosomes),
structural abnormalities (translocations, deletions
or inversions), or specific gene abnormalities (mutations).
These genetic diseases include Tay-Sachs, hemophilia,
sickle cell anemia, Thalassemia, Fragile X, Cystic Fibrosis,
Marfans, Duchenne muscular dystrophy and many others.
over 35 are also at increased risk of miscarriage caused
by aneuploidy. Preimplantation genetic diagnosis allows
the physician and embryologist to screen embryos for
many genetic diseases before they are transferred to
the mother's uterus.
choosing PGD must undergo an IVF cycle to produce embryos
that can be genetically screened. IVF involves the administration
of ovulation inducing drugs to the female, retrieval
of the eggs once they are mature, exposure of the eggs
to sperm so that fertilization can occur and culturing
of the embryos in incubators.
the embryo matures, usually after three to five days
of culture, a sample of its DNA is taken from one of
the embryo's cell. A small hole is made in the membrane
surrounding the embryo (the zona pellucida) using a
solution known as Acid Tyrodes, a small needle, or a
laser. This procedure does not damage the embryo.
the embryo's DNA is obtained it is examined using fluorescent
in situ hybridization (FISH), to screen for abnormal
numbers of chromosomes, and/or the polymerase chain
reaction (PCR) to screen for single gene defects. FISH
can also be used to identify a male and female embryo
which is important since some genetic diseases are linked
to the sex chromosomes. PCR is used to replicate certain
areas of the chromosome so that they can be examined
for the suspected disease.
PGD indicates chromosomal abnormalities, the embryo
will not be transferred back to the uterus. PGD can
also be used to identify gender for couples seeking
family balancing (but most clinics do not do this routinely).