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Preimplantation Genetic Diagnosis (PGD)

Preimplantation Genetic Diagnosis (PGD) is a new technology that can detect genetic abnormalities such as disease-
causing mutations and chromosomal abnormalities to prevent the conception of abnormal pregnancies, for example
Cystic Fibrosis. PGD has made the headlines recently in some controversial cases, including the use of PGD to prevent
transmission of adult-onset diseases such as Alzheimer’s; and the use of PGD to help conceive an HLA-matched child to
donate bone marrow for a sibling with Fanconi’s anemia. However, what is even more exciting than these headline
stories is that PGD may also be a very effective treatment option for women who suffer recurrent first trimester pregnancy
loss, for women with a history of a chromosomally abnormal pregnancy, and for women with age-related infertility. At this
time, only a few centers have significant experience with this technique, but this technology is spreading rapidly and will
likely become more routine within the next few years.

PGD requires the "creation" of embryos in the laboratory. Therefore, patients must undergo in IVF (in-vitro fertilization).
This technique involves ovarian stimulation of multiple egg-containing follicles using injectable hormones called
gonadotropins (Follistim, Gonal f, Pergonal, Repronex, etc). While the patient is under sedation or anesthesia, her eggs
are retrieved through the vagina using a needle and ultrasound guidance to aspirate the eggs. The eggs are then
inseminated with the husband’s sperm in the laboratory, using either the “conventional” fertilization or the ICSI
procedure. Once fertilization occurs, embryos are allowed to grow in the laboratory for a total of 3 days after egg
retrieval. After 3 days of culture, normal embryos will divide and should reach the 6 to 8 cell stage. At this stage of
development, each cell has the potential to become an entire human being and removal of a single cell will not harm the
embryo.

THE PROCEDURE
An embryo biopsy is performed by creating an opening in the zona pellucida, the “shell” around the embryo. A single cell
from the embryo is removed through this opening using gentle suction and a micropipette. The procedure is performed
using a special microscope with micromanipulators – special devices designed for delicate microscopic procedures. The
cell is then fixed upon a slide and the embryos that have been biopsied are placed back into an incubator to await the
results of the biopsy.

The analysis takes about 24 hours to perform and then the embryos that are normal by the analysis are then transferred
to the woman’s uterus on day 4 or 5 after the oocyte retrieval.

In addition to being able to identify chromosome abnormalities including Cystic Fibrosis Mutations, it is thought that PGD
improves the process of selecting embryos for transfer, allowing embryologists to choose embryos most likely to result in
a normal pregnancy. This may appeal to couples who have previously used IVF and were unsuccessful. By improving
embryo selection, and allowing fewer embryos to be transferred, PGD can also assist in reducing the frequency of high
order multiple births after IVF.

WHAT CAN BE DIAGNOSED via PGD
PGD can diagnose over 100 diseases,
below is a partial list of disorders that
can be diagnosed by using PGD
•        Cystic fibrosis
•        Fragile-X syndrome
•        Sickle-cell anemia
•        Polycystic kidney disease
•        Thalassemia
•        Huntington’s disease
•        Klinefelter syndrome
•        Tay-Sachs disease
•        Duchenne dystrophy
•        Lesch-Nyhan syndrome
•        Retinitis pigmentosa
•        X-linked disease mutations
•        Marfan syndrome
•        Turner syndrome
•        Hemophilia A
•        Kennedy disease
•        Treacher Collins syndrome
•        Charcot-Marie-Tooth disease

THE RISKS
The risks of PGD include damage to the embryo during the biopsy procedure. Embryo damage is an “all or none” phenomena. If an embryo is damaged,
it will stop growing. Embryos that continue to grow after the biopsy do not become abnormal as a result of the biopsy. If the embryo continues to grow
after PGD, it will not sustain any injury and will not be at greater risk for miscarriage or for birth defects. In fact as stated above, if the results of the PGD
are normal, these risks will be decreased.

SITUATIONS WHERE PGD IS INDICATED
PGD is indicated for patients with recurrent first trimester loss, advanced maternal age and for patients with a previous child or pregnancy with a
chromosomal abnormality (such as Cystic Fibrosis), PGD can reduce the risk of certain abnormalities in the patient’s next pregnancy. This may be an
attractive alternative to post conception testing for patients as they may be able to avoid termination of an abnormal pregnancy.