Prenatal Screening Program

1. What one should know
2. Chromosomal abnormalities
3. Current methods of approach
4. Screening procedure

1. What one should know

Every new life is as precious to its family as it is to society as a whole. Health, both mental and physical, is a great blessing to each and every one of us. Thus, preventing severe health conditions is the goal of modern medicine

One can confidently say that a normal, healthy baby will be born to the majority of pregnant women. However, in some cases, estimated at 3%, a physical abnormality will arise that may be due to changes in the genetic material of the foetus, either on a chromosomal or genetic level, sometimes occurring at the time of conception (where the ovum fuses with sperm), during embryo genesis (the development of the fused ovum/sperm into embryo) or inherited from one or both parents. It is under the first of these occurrences mentioned that give rise to trisomies 21, 18 and 13 that are a common cause of mental retardation.

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2. Chromosomal Abnormalities

Genes define our structure and control our functions. Approximately 30 000 genes are found amongst our 46 chromosomes that are tightly wrapped up in the nucleus of each of our cells (except red blood cells that have no nucleus and our germ cells; and sperm or ova that have 23 chromosomes in their nucleus that become 46 after conception). Each of these genes is responsible in expressing a certain protein correctly that will be part of a significant process in our bodies.

If, for any reason, a chromosomal aberration should occur whereby the loss, duplication or rearrangement of genetic material arises, significant syndromes usually result in the foetus, often causing a plethora of clinical conditions. The most common chromosomal abnormality is that of trisomy 21or Down’s syndrome, which is also the most common cause of severe mental retardation (amongst many other clinical complications presented), whereby a third copy of the 21st chromosome is made. It must, therefore, be emphasized that all pregnant women, have a risk of giving birth to a child with Down’s syndrome. This risk grows with maternal age.

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3. Current methods of approach


Chromosomal abnormalities in a foetus can be detected using cytogenetic techniques between the tenth and twentieth week of pregnancy depending on the type of procedure. However, since such procedures are invasive, they pose a 0.5-1% risk of miscarriage and are thus only offered to pregnant women that show an increased risk of carrying a faetus with a chromosomal aberration.

The risk is indicated by the screening test that is carried out during the first trimester of pregnancy. The test combines three factors to give an individual risk of the foetus having a specific chromosomal abnormality.

Two biochemical parameters are measured in the blood of the pregnant woman, namely that of free-beta human chorionic gonadotrophin (FβHCG) and pregnancy associated plasma protein-A (PAPP-A). These parameters, together with the woman’s age and an ultrasound measurement of the foetal nuchal transclucency, are fed into an algorithm to give the final risk. The sensitivity of this test in detecting trisomy 21 is approximately 85%, in other words, with the application of this procedure an estimated 85% of actually affected pregnancies will be detected, as it must be stressed this is not a diagnostic test. This method replaced the “triple test” at the start of 2001 that was carried out in the second trimester of pregnancy, again offered by the Center for Preventive Paediatrics (then known as the Mental Retardation Prevention Center).

Deciding whether to terminate an affected pregnancy or not, can only be taken by the fully informed parents.

The Special Preschool Education Unit of the Theotokos Foundation, together with the Center for Preventive Paediatrics, offer diagnostic, therapeutic and educational services to children born with chromosomal abnormalities, as well as counseling and psychosocial support to their families.

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4. Screening Procedure

When the pregnant woman visits the gynaecologist between the 9 ^th and 13^th week period of pregnancy (preferably around the 10th week) she will have some blood withdrawn. Her doctor will also take down some readings of the pregnancy on a special report. It is the patient’s responsibility to deliver without delay the sample and form to the premises of the Center for Preventive Paediatrics:

• by personally handing it over if she lives in Limassol by 3pm,
  
• by taking it immediately to a specific courier service in her district, prepaid for by the Center.

The Center operates five days per week, excluding weekends, from 8am until 3:30pm continuously. It is most important that the samples be handed over to the courier service by 11:30am (in Paralimni area they should be handed over by 09:30am). Delivery in person should not be done after 2:30pm.

The Center’s lab then performs the biochemical test on the blood sample and sends the results back to the gynaecologist who in turn ensures that the sonographic measurement of the foetal nuchal translucency is done. This can only be performed between 11 –13⁺⁶ weeks by a doctor – affiliated to the Cyprus Branch of the Foetal Medicine Foundation (FMF). The combined result-risk based upon the sonographic measurement and the biochemical test is sent both to the requesting gynaecologist and the Center for Preventive Paediatrics. The former will offer genetic counseling where appropriate.