The characteristics that define an early-stage miscarriage vary and doctors and ultrasound equipment could be misdiagnosing miscarriages resulting in inadvertent termination of pregnancy.
A recent study published in Ultrasound: Obstetrics and Gynecology found that one in 200 diagnosed miscarriages, which result in the women taking pill or having surgery to remove the fetus from her uterus, are in fact false and the fetus is still alive.
New Scientist reports:
In the UK, an empty gestational sac – the structure in which an embryo usually grows – with a diameter greater than 20 millimetres is classified as a miscarriage, while in the U.S. a diameter of 16 millimetres is used.
If a smaller sac is detected which appears empty, the woman will usually be advised to have a second scan seven to 10 days later. If the sac has not grown in that time it is assumed that the woman has miscarried.
Seeking out the reliability of these cut-off characteristics and potentially to define more reliable characteristics, Tom Bourne from Imperial London College studied 183 women who were considered to have miscarried according to an ultrasound reading. What he found was that, 175 women were correctly diagnosed while eight women's children were still living, even though the 16 millimeter cut-off criteria -- the measure used in the United States -- had diagnosed them as miscarried.
New Scientists continues:
"There's no doubt that on the basis of one scan, the potential for misdiagnosis exists," says Bourne. "Some women seeking reassurance with pain or bleeding in early pregnancy may be told that they have had a miscarriage, and choose to undergo surgical or medical treatment when the pregnancy is in fact healthy."
Bourne also emphasises that the findings are only relevant to a subset of miscarriages. "What I'm absolutely not saying is that it is likely that if someone has had surgery for miscarriage, they have had a misdiagnosis," he says. "The majority of women come in with bleeding, where the miscarriage is actually declaring itself. We're looking at patients with a diagnosis based on ultrasound, which is a subset of women, and we're only talking about the ones who are near these cut-off levels."
The Daily Mail reports that a third of the 500,000 miscarriages in the United Kingdom are diagnosed using this method:
[...] they estimated that errors could lead to 400 women with healthy pregnancies being wrongly told their baby has died each year.
Bourne recommends the guidelines be stricter and that women concerned their pregnancy may still be viable to wait a week and get rescanned. The Daily Mail goes on to state that the Royal College of Obstetricians & Gynecologists is reviewing guidelines already and will take these findings into account.
The American Pregnancy Association states that in the United States about 600,000 women experience miscarriage each year. The National Maternity Hospital states on its website that it follows the Royal College of Obstetricians & Gynecologists in the United Kingdom and that a similar update guidelines was made in 1995 to help ensure viable pregnancies were not unnecessarily terminated.