Prevention of Genetic Diseases

Counselling and prenatal diagnosis

Most pregnancies end in the birth of a child who is normal and healthy and have a good quality of life. However about 3% of pregnancies result in the birth of children with abnormalities.

It is the constant endeavor, of those in the medical profession who are charged with the responsibility of caring for pregnant women, to look for clues which might suggest that the foetus (the unborn baby in the mothers womb)might be at risk for a serious medical disorder. About 20 years ago even if such a suspicion was raised doctors could do very little to prove or disprove their doubts. They therfore had very little evidence to advise the parents in a meaningful way. In a short span of twenty years technology has transformed this scene.Today with advances in molecular biology and safe techniques for obtaining material from a pregnancy, many conditions including genetic diseases can be identified in early pregnancy.This gives the parents an opportunity to make an informed choice regarding the future health of their offspring.Since the majority of the pregnancies end in the birth of normal children one cannot subject every pregnancy to such invasive studies. Therfore a number of screening techniques are offered to pregnant women to try and identify those who will benefit the most from further detailed studies. The couple who will most benefit from these methods are those who are at risk for a specific genetic disorder.To determine the 'at risk' couples there are a number of different pointers. Age of the mother for example is an important criteria.Women above the age of 35 have a greater risk for having a child with Down's syndrome (Mongolism). Certain ethnic groups are at a greater risk for some inherited diseases. Amongst the Asian communities a couple belonging to the Gujarati,Sindhi or Punjabi community have a greater risk for an inherited blood disorder called Thalassemia.
If a previous child was born with an abnormality it may be possible to avoid a repitition of the same in the next pregnancy. This needs the knowledge of what is the type of disorder in the previous child. Parents with children who have an abnormality should request their doctors to try and establish this diagnosis. Without that information it is often impossible to know what disease to look for in the next pregnancy. Many of these children with abnormalities succumb to complications and their condition remains undiagnosed. When the child is alive it is often possible to come to a conclusion about the disease and it is the best time to undertake such an excecise. In some couples there may be a past history of having had more than three miscarriages or loss of a foetus midway in pregnancy (IUD= Intrauterine death), or stillborn child or loss of a child in early childhood (Neonatal Death) Even here couples must request the doctors attending to try and see if a reason can be attributed to such a loss. An abnormality in a child in some other family member may suggest that this could be repeated in the present pregnancy. An inadvertant use of a drug or having an X-ray taken without realising that a pregnancy has begun or exposure to an infection like Rubella can have serious effects on the foetus. Today it possible to test and assess the chance of a foetal exposure to infections like Rubella,Chicken Pox or Toxoplasmosis.
Complications during pregnancy like low growth of the child,called Intra Uterine Growth Retardation (IUGR) and/or reduced amount of amniotic fluid (Oligohydramnios) may suggest the possibility of a genetic (chromosomal) disorder. Most pregnancies in contemporary times have at least one ultrasonographic examination. During these routine sonography tests one may pick up evidence which might suggest the presence of a genetic disease or developmental disorders. Similarly most pregnant women are offered special blood tests at 10 weeks of pregnancy called "First trimister marker" and at 15 weeks of pregnancy called the 'Triple marker'.These are useful tests which may arouse a suspicion. However,many of these are only "screening" (not diagnostic) tests and are not conclusive evidence of an abnormality.A screening report which suggests the possibility of a genetic disorder may need to be followed up with a procedure like Chorion villus sampling (CVS) at 10 weeks of pregnancy or by Amniocentesis after 15 weeks to prove or disprove the doubts raised and to get a definitive answer.It is worth repeating this fact that a positive screening report does not necessarily mean that the foetus is abnormal. It must be considered as an opportunity to be cautious. One does not want to regret after the child is born that an opportunity was presented by the screening tests to be cautious and one failed to heed to this warning. Many of these problems lead to life long suffering for the child and the parents and it is perhaps prudent not to miss an opportunity to ensure that the foetus indeed is normal. A note of warning, a negative screening report does not rule out all known abnormalities but may simply suggest that the risk is low. The procedures like CVS and Amniocentesis are safe if they are carried out under sonographic guidance at the appropriate time by an expert in a specially designated sterile area.The loss of a pregnancy following these procedures are low and for a trans abdominal CVS this risk is as low as 0.5% in our hands while for amniocentesis it is even lower at 0.3%

There are thus many methods of identifying an 'at risk' pregnancy and offering counselling and prenatal diagnosis.We are ofcourse far away from doing a single test in pregnancy and be able certify that the foetus is completley normal and free of all known diseases. The knowledge in this field is ever expanding and each day improves our ability to diagnose conditions which were not possible earlier. The logical way forward would be to identify and also "correct" these disorders (foetal therapy). That day may not be too far away.

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Dr P G Natrajan MD,DGO,FRCOG