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A False Positive for Miscarriage
Though it would seem obvious when a woman has a miscarriage even early in pregnancy, the truth is that it’s not as straightforward as one might think. The guidelines doctors use to determine whether a miscarriage has occurred or not are not as accurate as they should be, according to a recent study. This can mean that perfectly healthy pregnancies may be receiving unnecessary intervention when doctors mistakenly believe they have ended.
When women experience bleeding early in their pregnancy, it’s possible that miscarriage has occurred. To find out, doctors use ultrasound to measure the gestational sac and the embryo at one time point, and then follow up with a second measurement one week to 10 days later to see whether growth has occurred. The new studies looked at how – and how much -- fetuses change over time in the early weeks of pregnancy.
The team determined that the cut-offs conventionally used by doctors to determine if the fetus is growing don’t leave enough room for error. Depending on the doctor making the measurement, up to a 20% variation can exist for one fetus at one point in time. Therefore, if the first measurement overshot the actual size of the fetus, and the follow-up measurement undershot it, a doctor could erroneously conclude that zero growth had occurred.
What’s more, according the new research, even perfectly healthy fetuses can show no growth between the two measurement time points.
“These errors could lead to a false diagnosis of miscarriage being made in some women," said a coauthor of the study, Anne Pexsters, in a news release. By using more lenient measurement guidelines, doctors could reduce or hopefully eliminate the possibility of ending pregnancies that are in fact healthy.
“By identifying this problem we hope that guidelines will be reviewed so that inadvertent termination of wanted pregnancies cannot happen. We also hope backing will be given to even larger studies to test new guidelines prospectively,” says co-author Tom Bourne. “Currently there is a risk that some women seeking reassurance with pain or bleeding in early pregnancy may be told they have had a miscarriage, and choose to undergo surgical or medical treatment when the pregnancy is in fact healthy.”
He adds that since miscarriage can be a traumatic situation, doctors need to work hard to reduce the possibility of misdiagnosis. "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,” he says. “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.”
Unfortunately, it may take time to redesign the guidelines. But hopefully as more doctors become aware of the potential errors that can occur as a result of the current ones, they will be more cautious in diagnosing miscarriage, until it is absolutely certain to have occurred.
A series of studies on the subject will be published in the current issue of Ultrasound in Obstetrics and Gynecology. Bourne is a researcher at Imperial College London.
October 18, 2011