Is screening for Fetal Abnormalities the right decision in pregnancy?

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Screening for Fetal Abnormalities

It is important to draw a clear distinction between screening examinations which are offered to all pregnant women and specific examinations which are performed selectively because of high risk features. Screening procedures should be simple, inexpensive and completely safe.Family history, ultrasound and maternal serum biochemical testing are typical examples of screening tests. Some specific tests may carry some risks to the pregnancy, a risk that may be justified by the usefulness of information obtained and the risk of the fetus having a major problem of some sort.

  Down syndrome baby

Examples of such tests are amniocentesis, chariot villas sampling (CVS) or fetal blood sampling come into this category of test.Whether a test is of screening or specific type, it is important that a pregnant woman understands its nature and significance and that she makes an informed decision to undergo the test or not. Initial approach to the detection of fetal anomalies need not involve sophisticated tests.

The initial screening begins at the clinic when the woman presents first for antenatal care or even beforehand. The mother’s age, medical history, recent drug treatment and alcohol intake are very important elements in fetal well-being.

The use of ultrasound at each trimester is still a contentious issue. Some countries practice it as a recommended guidelines while others do not.  However most hospital where maternal serum screening is offered have introduced a simple early scan for dating to improve interpretation of biochemical tests. Recently, there has been a growing interest in using this scan as a screening test for fetal anomalies, determination of chorionicity in multiple pregnancies and detection of chromosomal Abnormalities.

The fetus and placenta are responsible for numerous changes in the maternal circulation which apart from the well-known adaptational haemodilution, this includes presence of fetal cells and significant rise in a-fetoprotein(AFP)  and human chorionicity gonadotropin (hCG). In the meantime the mainstay of non-invasive screening for chromosomal abnormalities and neural defects have been biochemical testing of maternal serum.

Screening for Down syndrome

Low level of maternal AFP is a signal that the fetus has a major chromosomal abnormality although there is considerable overlap with values from normal pregnancies. This finding has been exploited to screen for fetal  Down syndrome. Notably, uE3 levels tend to be higher in association with Down syndrome or Tipple screen (AFP, uE3 and hCG) .

The results are adequately interpreted and compassionate counselling is needed before and after the screening.

This is a sensitive and complex task for triple screen because of the perception of the risk which varies significantly among individuals and societies. The decision to screen for Down syndrome is entirely the woman’s choice even when doctors notice abnormalities. A study shows that 10% of women would not have wished amniocentesis performed at the risk of Down syndrome at 1 in 10 chances, while 20% would have wished for the procedure performed with a Down syndrome risk for as low as 1 in 2000.What about you? Would you or not?