Current guidelines that help clinicians decide whether a woman has had a miscarriage are inadequate and not reliable, and following them may lead to the inadvertent termination of wanted pregnancies, according to a series of papers published in the international journal, Ultrasound in Obstetrics and Gynecology.

“This research shows that the current guidance on how to use ultrasound scans to detect a miscarriage may lead to a wrong diagnosis in some cases. Health professionals need clearer evidence-based guidance to prevent this happening,” Professor Basky Thilaganathan, MD, director of the fetal medicine unit at St. George's, University of London and editor-in-chief of the journal, said in a statement.

A miscarriage is often confirmed by using an ultrasound scan to see whether there is any sign of a pregnancy sac or embryo in the womb, and women understandably expect that when a diagnosis of miscarriage is made there is no room for error.

Four studies based at Imperial College in London; Queen Mary, University of London; and the Katholieke Universiteit Leuven in Belgium, indicated multiple concerns about existing guidelines. These are:

• Existing guidelines for mean gestational sac diameter (MSD) and embryo crown-rump (CRL) length used to determine miscarriage vary from 13 to 22 mm and 3 to 8 mm, respectively. After conducting an observational cross-sectional study and reviewing false-positive diagnoses, the researchers suggested an MSD cut-off of >25 mm and a CRL cut-off of >7 mm to minimize the risk of a false-positive diagnosis of miscarriage.
• A second study found overlap in MSD growth rates between viable and non-viable intrauterine pregnancies of uncertain viability. When there is doubt about the diagnosis of miscarriage, current guidance suggests the pregnancy sac should be re-measured seven to 10 days later. If the sac does not grow, it is assumed that a miscarriage has occurred. However, the study found that perfectly healthy pregnancies may show no measurable growth over this period of time. No cut-off exists for MSD growth below which a viable pregnancy could be safely excluded, the researchers concluded.
• A systematic literature review to evaluate the accuracy of first trimester ultrasound in the detection of miscarriage identified a lack of high-quality data to inform guidelines for early pregnancy demise. The researchers called for an appropriately powered, prospective study using current ultrasound technology and an agreed reference for viability or non-viability.
• The final study revealed variation in the size of gestational sacs of up to 20 percent when different clinicians measure the same pregnancies. If the first measurement over-estimated the sac size and the second measurement some days later underestimated it, then a physician might incorrectly conclude that no growth had occurred. “These errors could lead to a false diagnosis of miscarriage being made in some women,” Anne Pexsters, MD, of the Katholieke Universiteit Leuven, said in a statement.

“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,” Tom Bourne, PhD, from Imperial College London said in a statement. “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.”