Genetic screening refers to the testing of an individual or group of people to see if they carry a particular gene or genes. Genetic screening of human embryos (the term used to describe the early stages of fetal growth, from conception to the eighth week of pregnancy) is becoming increasingly common, with the development of new technologies that allow more accurate methods of testing the genes present in an embryo. This testing of embryos may provide significant benefits to produce healthy babies. However, the topic of genetic screening is also characterized by a soaring level of controversy, as it is seen by many as being a challenge to human ethics.

Uses of Genetic Screening

Uses of Genetic ScreeningGenetic screening has most widely been used to test chromosomally diseased embryos, such as ones with Down's Syndrome, as well as other genetic disorders that include:

  • Tay-Sachs disease
  • Cystic fibrosis
  • Sickle cell disease
  • Huntington's chorea
  • Muscular dystrophy
  • and Cooley's anemia
Similarly, genetic screening can be used to screen genes that predispose an individual to breast or colon cancer, as well as to determine the gender of the embryo. This ability allows the testing of sex-chromosome-linked diseases such as hemophilia. In addition, the procedure may be used to select a child who may be a compatible donor for a sibling with potentially fatal diseases such as particular anemias and leukemias. The PGD is also seen as an infertility treatment, as the rates of multiples (twins, triplets) are much higher for women undergoing fertility treatment. Women suffering from infertility often request for assisted reproductive technology to increase the chances of pregnancy.

external image embryo_sm.jpg

PGD is recommended in most fertility clinics for patients with:

  • Recurrent miscarriages (usually more than 2)
  • Women 35 and older who produce 6 or more embryos with IVF
  • Family history of chromosomal conditions or history of X-linked disease
  • Unexplained infertility
  • 2 or more unsuccessful cycles


Methods of Embryo Screening

Methods of Embryo ScreeningEmbryo biopsy, or Preimplantation Genetic Diagnosis (PGD), is the most common method of genetic screening embryos. The PGD tests the early-stage embryos that are produced through in vitro fertilizationin vitro fertilizationin vitro fertilization (IVF) for the presence of a variety of conditions. The PGD involves the extraction and analysis of one cell from the embryo in its eight-cell stage, around two or three days after conception through in vitro virtilization. At this stage, the embryo's cells have not differentiated into specific body tissues, and therefore there is no damage done to the resulting embryo. The selected cell’s genes are replicated using a polymerase chain reactionpolymerase chain reactionpolymerase chain reaction to be studied for genetic defects while the embryo itself remains unaltered and continues its growth. An embryo that is proved to be healthy can then be implanted in a woman's uterus to allow development into a child. Thus, the process does not involve the manipulation of genes in embryos, but rather it selectsselects among embryos.

external image 12GENETICS.jpg

The PGD requires genetic material from the embryo or the polar body, a smell section of an egg that contains the set of chromosomes complementary of those present in the oocyte. The polar body can be examined using a procedure called Flourescence in Situ Hybridazation (FISH), so that the chromosomal make-up of the oocyte may be deduced. It is interesting to note that 85% of embryo aneuploids (extra or missing chromosomes) are due to the femal oocyte, where as the much smaller remainder is of sperm origin. FISH can detect large chromosomal abnormalities, such as aneuploidies, the gender of the embryo, as well as unbalanced chromosonal translocations. During the procedure of FISH, DNA probes are labeled with colored florescent tags which light up to allow viewing of specific chromosomes or genes under a microscope. Such analysis of chromosomes has up to a 10% error rate. However, in cases where the abnormalities are much more subtle, such as on the scale of single genes or even DNA bases, a highly speciailzed technique, like the PCR, is required. This method relies on the fundamental principles of the genetic code, specifically on the complementary base pairing of DNA.

For information on the development of the PGD, go to :



Ethical Issues

Most couples desire a child without a disease. Some have more specific preferences, such as gender or appearance. All this is possible with Embryo screening. The only problem, this option is loaded with ethical and moral issues.

1) What happens to the undesired embryos?

The undesired embryos are destroyed or frozen. A strong argument against this is that life begins at conception and that this process is the killing or wasting of human life.

2) Embryo Screening is interfering with nature!

Each time the parents visit the doctor, they are interfering with nature and its natural process. Many people believe that women should have natural babies, instead of being able to chose them. Many ethicists’ fear that people are increasingly seeking “designer babies”, not just free of medical defects but also possessing certain desirable traits.

3) What about respect?

Often times, embryo screening determines whether or not parents will keep the child. Boys tend to be preferred over girls, igniting a feminist issue. It shows a lack of respect for human life e.g. “we chose you because you satisfy these conditions” It sends the message to disabled people that they are not worthwhile.

4) What do the children want?

Many children, when surveyed, stated that they’d rather be born with a disease than not be born at all.

5) The positive ethical issues…

Parents use this to help children avoid having illnesses. Would you accept your child if they couldn’t function? What if you could do something about it?

6) Where’s the line?
Once you screen for a disease, what’s to stop you from screening for other things?

-Shi-Hua Chin




Embryo Screening Controversy

There are many couples who have specific preferences about their child, such as those who do not want their children to have a disease, or want to choose the gender. Now couples can have that option through vitro fertilization clinics which offer pre-implantation genetic diagnosis (the testing of embryos through in vitro fertilization). About 74% of clinics offer PGD, mostly for disease, however others also use it for more controversial purposes, such as sex selection, or to have a child that is an immunological match for another ill child of theirs so that it can be a stem cell donor.

There are some that believe that the procedure of PGD (taking one cell out of an eight-cell embryo and sending it out to multiple clinics to be analyzed) is controversial, for those who believe that life begins at the moment of conception see this is a killing of human life.
People also believe that PGD sends out the message to disabled people that they are not worthwhile, however some still believe that it is perfectly ethical to want your child to be born without diseases. PGD raises difficult issues, as it is hard to distinguish where to draw the line. While it is understable to not want a child to be born with diseases, once the cell is screened, people may be tempted to detect for other specifics about their unborn child, and with the rate of scientific advances, who knows what this may lead to many years down the line.
Michelle FlorCruz