By James Gallagher
14 October 2011 Last updated at 01:11
Some pregnancies are being terminated unnecessarily after an incorrect diagnosis of miscarriage, say doctors.
They say there is too much room for error in ultrasound scans in the first six weeks, which wrongly label a small percentage of embryos as miscarried.
The true scale of the problem is unknown but researchers said it was “hard to see how there can’t be women having misdiagnoses being made”.
Guidelines are currently being reviewed.
The study suggested the current rules “could lead to 400 viable pregnancies potentially being misclassified”, however the researchers said this was an educated guess with no evidence of how many would lead to a termination.
Miscarriage is very common, affecting one in five pregnancies.
If a women experiences pain or bleeding early in the pregnancy, around five to six weeks, they will have an ultrasound scan.
Two results would suggest a miscarriage, which could then lead to a decision to terminate the pregnancy:
an embryo greater than 6mm in length, but without a heartbeat
a pregnancy sac greater than 20mm, but with no visible embryo
A series of papers published in Ultrasound in Obstetrics and Gynaecology questioned the thresholds.
One paper reviewed the evidence for the guidelines and said they were based on poor evidence.
Another reported significant variation in the measurements made by different clinicians, which could in theory change the diagnosis.
Tests on 1,060 women whose pregnancy was in question showed the 20mm rule would diagnose about 0.5% of cases as miscarriages when they were in fact healthy.
Prof Tom Bourne, from Imperial College London, told the BBC: “We found that the cut-off values were not entirely safe because they can be associated with a misdiagnosis of miscarriage in a small number of cases, and our view is that there shouldn’t be any risk.
“I think a significant number is one, frankly. I think anyone who has a diagnosis of miscarriage and potentially has surgery would expect that that diagnosis is right.”
He argues the cut-offs should be about 25mm instead of 20mm for the sac and 7mm for an embryo without a heartbeat. He also wants a greater emphasis on repeat scans.
He said: “There’s not a medical cost to being more cautious in what we’re doing.”
Prof Siobhan Quenby, from University Hospital Coventry, welcomed greater attention and clarity on the issue, but said: “I really don’t think many mistakes are being made.”
She said people were aware of issues with the guidance and if there was any doubt, further tests, not a termination, would take place.
It is “very common that people come back for a second scan”, she said.
For those with a miscarriage diagnosis, she said that in the majority of cases there would be no medical intervention. About 30% would take tablets or have surgery to end the pregnancy.
Dr Mark Hamilton, consultant gynaecologist at Aberdeen Maternity Hospital, said the findings “reinforce the need for clinical staff to continue to exercise great care in the diagnosis of non-viable pregnancy to minimise the risk of misdiagnosis.
“Women should continue to be managed expectantly without the need for medical treatment or surgery until the diagnosis of non-viability is established with certainty.”
The National Institute for Health and Clinical Excellence is currently developing guidelines for the care of women who experience pain and bleeding in early pregnancy. There is already guidance available from the Royal College of Obstetricians and Gynaecologists.
This will include the role of ultrasound in determining the viability of a pregnancy and will draw on this research. New guidelines are due in November 2012.
The Royal College of Obstetricians and Gynaecologists welcomed the studies.