UK researchers have recommended that pushing back the timing of a second ultrasound scan in women thought to have miscarried may help to avoid the termination of healthy pregnancies.
Current national guidelines on the diagnosis of miscarriage may still be associated with misdiagnoses, and should be reviewed in light of new evidence, argue the researchers.
The Royal College of Obstetrics and Gynaecologists guidelines recommend a miscarriage diagnosis based on an ultrasound scan measurement of the gestational sac diameter (GSD) and the embryo’s crown-rump length (CRL).
“Guidance on timing between scans and expected findings on repeat scans are still too liberal”
Guidelines on the cut-off values for these measurements were updated in 2011, following concerns that the older recommendations were based on inadequate evidence and leading to misdiagnoses.
But the researchers argue that the guidelines now also need to be updated with new criteria for when the initial scan is inconclusive and a repeat scan is needed – as a result of the embryonic and gestational sac sizes being too small.
A repeat scan is recommended, usually one to two weeks later, but this guidance is based on expert opinion rather than evidence.
Professor Tom Bourne, from Imperial College London, and colleagues set out to determine new recommendations for the second scan.
They examined the ultrasound scans of 2,845 women admitted to seven early pregnancy units in the UK during 2011-13.
Women were admitted due to vaginal bleeding, pain, severe morning sickness or a previous miscarriage or ectopic pregnancy.
Based on the examination of these ultrasound scans, the authors specifically called for a repeat scan between seven and 14 days after the initial scan depending on the size of the GSD, CRL and presence or absence of a heartbeat.
“Guidance on timing between scans and expected findings on repeat scans are still too liberal,” said the authors in the British Medical Journal.
“Protocols for miscarriage diagnosis should be reviewed to account for this evidence to avoid misdiagnosis of miscarriage and the risk of terminating viable pregnancies,” they added.