Research has led to claims that up to 400 healthy fetuses may be aborted every 12 months.
An estimated 500,000 women have miscarriages in the UK each year.
Usually, doctors perform an ultrasound scan to measure the size of the gestational sac.
If it appears empty, or a well-developed embryo shows no heartbeat, a diagnosis of miscarriage is made.
If there is any doubt, guidelines recommend doctors re-measure the gestational sac seven to ten days later for confirmation.
However, a study led by Professor Tom Bourne from Imperial College London found that perfectly healthy pregnancies may show no measurable growth over this period of time.
Research also revealed a 20% variation in the size of gestational sacs reported when different clinicians measure the same pregnancies.
The study states errors ‘could lead to 400 viable pregnancies potentially being misclassified’.
Professor Bourne said: ‘For most women sadly there is nothing we can do to prevent a miscarriage.
‘But we do need to make sure we don’t make things worse by intervening unnecessarily in on-going pregnancies.
‘We hope our work means that the guidelines to define miscarriage are made as watertight as we would expect for defining death at any other stage of life.’
Professor Bourne has called for the guidelines to be reviews so ‘inadvertent termination of wanted pregnancies cannot happen’.
He said he also hopes for further backing to carry out more in-depth research on the subject.
The study has been published in the international journal
Ultrasound in Obstetrics and Gynecology.
