Single diagnostic test is standard practice, says National Maternity Hospital
Simon Harris wants external review in case of wrong finding of fatal foetal anomaly
Prof Fergal Malone, Rotunda Hospital master: because the rapid test can give a false positive if there is no ultrasound abnormality most laboratories recommend to wait for the full two weeks.
The National Maternity Hospital says it follows standard practice in carrying out terminations where requested by parents following a single diagnostic test showing a fatal foetal anomaly. UK and international guidelines suggest confirmatory second-test results should first be obtained.
The hospital also says it is “moving towards” setting the terms of reference for an independent review into the case of a termination carried out for reasons of fatal foetal anomaly, where a later test showed no anomaly.
Minister for Health Simon Harris believes an appropriate external review is warranted and it is important to await its findings, a spokeswoman said. “The Minister’s overriding concern is for the couple involved and respecting their privacy,” she added.
The termination was carried out last March after an initial rapid prenatal test showed a woman’s baby had a chromosomal abnormality, though this was not seen on the ultrasound. Afterwards, the results of a second test came back normal.
The hospital says this is the first time in over 1,200 cases such a situation has arisen. The test was processed in a UK laboratory which has thus far not identified any other such false positives.
The woman underwent the diagnostic testing after an initial blood screening showed her baby had an elevated risk of Edwards syndrome (Trisomy18), a rare fatal foetal anomaly.
The test, based on a sample taken from the placenta, is regarded as 99 per cent accurate, with a false positive rate of about 0.15 per cent. In exceedingly rare cases, there is a divergence between the cells in the placenta and the cells in the foetus. This can give rise to a false positive, where the test gives an abnormal result but the baby does not actually have an abnormality.
A rapid form of the test known as QF-PCR that can identify Edwards syndrome takes five days. Cells from the sample can be grown to look at all the baby’s chromosomes and give information about other anomalies but this takes two weeks to process.
In the UK, the national screening programme recommends that where the rapid result indicates the baby may be affected by Edwards syndrome, and where the ultrasound is normal, “a culture result should be used to confirm the QF-PCR result prior to any decision being made regarding ongoing care or termination of the pregnancy”.
Separately, the International Society of Ultrasound in Obstetrics and Gynaecology practice guidelines state that, in some settings, the use of QF-PCR has replaced the full karyotype.
“However, inaccuracies of the rapid testing results (false positive or false negative) are reported occasionally. On this basis, abnormal rapid testing should be confirmed by metaphase culture or should be associated with ultrasound anomalies before making clinical decisions regarding continuation of the pregnancy.”
Rotunda Hospital master Prof Fergal Malone said because the rapid test can give a false positive if there is no ultrasound abnormality most laboratories recommend to wait for the full two weeks.
“But some patients are not prepared to wait the two weeks and want to continue to termination. Generally we recommend that they get the total picture.”