Abstract:
Prenatal genetic screening is an integral part of general antenatal care and is regarded as standard of care for all pregnant
women. All pregnant women < 20 weeks gestation should be offered some form of genetic screening and this should be
discussed in an extensive pre-test counselling session. Late screening (after 20 weeks) may also be offered but will be
limited by management options. Cell-free DNA testing has added another dimension to the landscape of prenatal
screening but has to be appropriately used for the correct indication. Interpretation of risk for Down’s syndrome is a critical
component of the screening process. A guideline would be to regard screening risks in absolute terms as there is no
provision made to interpret risk in relative risk terms. An important safeguard to overcome the “relative risk” conundrum
would be to inform all patients during pre-test counselling of an intermediate risk category generally between 1:300-1:1000
where cfDNA testing may be considered, at the parents’ own discretion. If the screening risk is <1:1000, no further testing
is advised as this risk is deemed very low. A screening risk for Down’s syndrome >1:300 will be deemed high risk, as is
presently the case.
