Download Courage Chibiya BSc Computer Science (Industry)

1 Introduction
Prenatal screening covers the procedures that are available to pregnant women in order to find out
those at risk of having a child that is affected by congenital disorders, especially chromosomal
abnormalities such as Down syndrome. Screening is mainly carried out using biochemical markers
(hormones) or ultrasound (sound waves) techniques. Recent developments in prenatal screening such
as new ultrasound and biochemical markers and the generation of likelihood values at different stages
of the calculation process are not available in existing software (Wilson, 2006). In addition, as
screening becomes more widespread, screening centres increasingly wish to be able to use highly
advanced systems that allow them to calculate risk results from wherever they may be in the world.
The aim of this project is to develop such a system for calculating the risk likelihood value.
1.1 The Problem Domain
Over the past two decades, prenatal screening for fetal defects has become a standard part of prenatal
care (Kristol, 1993). Tests conducted during the first trimester of pregnancy are designed to detect a
wide range of genetic and other disorders and to give prospective parents the option of obtaining
abortions if defects are diagnosed (Cuckle, 1997). This development has been heralded as a
breakthrough in the age-old battle against illness. Others consider it as more than that: an instrument
to improve society. There are invaluable benefits to screening, lives can be saved or improved and
major cost savings incurred by the health system and families. Like any major medical development
likely to occur in our age, prenatal screening has its own share of controversial consequences. The
issues surrounding the morality of screening are the stuff of moral philosophy (Kristol, 1993) and
agreement on the acceptable social consequences is difficult to achieve, however that should not
obscure the benefits that can be gained from prenatal screening.
The most common form of prenatal screening is ultrasound screening; about 80% of all pregnant
women receive ultrasound screening (Jones, 2005). This method uses sound waves to generate a
sonogram or image of the fetus in the womb. The main purpose of this test is to establish the
gestational age of the fetus and in addition other defects such as malformed organs might be noticed.
There are several indicators that can be found during ultrasound screening which have a significant
association with chromosomal abnormalities. These “markers” in combination with other biochemical
markers can be used to discriminate between unaffected fetuses and positive ones (Smith-Bindman,
2001). Examples of ultrasound markers are nuchal translucency (NT - the thickness of the nuchal area
at the back of the neck) and neuroblastoma (NB), a cancer that affects nerve cells of immature or
developing cells such as those found in a fetus.
In addition to ultrasound screening, physicians carry out serum screening - a procedure in which they
check a mother’s blood to obtain certain measurements such as alpha-fetoprotein (AFP), unconjugated
estriol (UE3) and human chorionic gonadotropin (HCG). The blood test results of these independent
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