New antenatal screening tests: communication challenges
Dr Peter Henderson MB ChB, FRANZOG, FRCOG, Senior Medical Advisor, Avant
Monday, 24 November 2014
With Australian women in the early stages of pregnancy now able to send their blood samples overseas for cell-free DNA testing, we look at the medico-legal implications this can raise for you.
The introduction of testing for aneuploidy involving chromosomes 21.18 and possibly 13, using the identification of cell free foetal DNA in maternal blood, brings a new dimension to the identification of triploidy in low as well as high-risk women during the first few weeks of pregnancy.
While Australians are now submitting blood samples for testing in the USA and Hong Kong, these tests are not covered by Medicare, nor recommended for low-risk women by some bodies, including the American College of Obstetricians and Gynaecologists.
The test, based on the polymerase chain reaction (PCR) probing of cell-free foetal DNA extracted from a maternal blood sample, has been shown to have a high specificity and sensitivity. However, the test is not always reliable, and like the chorionic villus sampling (CVS) test, mosaicisim of placental tissue may be identified as representing the foetus. Therefore, the test can be positive in the presence of a normal foetus.
Additionally, the test is not always possible as the percentage of cell-free foetal DNA may be low in some women, such as those with a high Body Mass Index (BMI). Therefore, a positive test should be followed up with diagnostic confirmation.
For most obstetricians, a challenge has been to explain to patients, in layman’s terms, the difference between a diagnostic test to establish the presence of a disease or condition and a screening test to detect early risk factors.
The concept of risk as it applies to an individual, also varies enormously from patient to patient. These factors have led to a steady stream of civil claims and complaints to disciplinary bodies concerning Avant’s members in the past and the new cell-free DNA test is no exception.
Avant has started to see cases where members have received patient complaints alleging they failed to offer the full range of tests, or adequately explain the limitations of tests offered.
Obstetricians can reduce their risk of an unhappy patient by explaining to them any possible tests relevant to their particular situation. It’s important to not only stay up-to-date with recent developments in this area, but to then devise a strategy that enables you to provide your patients with pertinent information – both verbally and in print form.
Any discussion regarding cell-free DNA tests should be recorded in the medical record. All oral advice should be augmented by written information, such as pamphlets provided by pathology services. A record should be made of the written information given out, including the version number, if relevant. Any particular concerns of the patient should also be recorded and at the next visit, the patient’s response to the question: “Have you read the information and do you have any questions?” should be noted.
The new test appears to hold promise in detecting susceptibility to pre-eclampsia and the Rhesus (Rh) factor status of the foetus, and its use may extend to other aneuploidies and gene mutations in the future.
The ability to identify a Y chromosome also has implications for the thorny issue of those wishing for sex selection, but may also become useful in managing carriers of X-linked disease and detecting genetic disease.
The rapid rise in knowledge associated with the sequencing of the human genome, and the translation of this into clinical practice, is likely to put greater pressure on obstetricians to assess and advise their patients in this realm.
Refer to Avant’s Medico-legal risk and your practice: Checklists for Obstetrics and Gynaecology.