How Often Do Third-trimester Growth Scans Detect Foetal Anomalies?

Pavankumar Kamat

June 15, 2020

Routine third-trimester growth scans detected a previously undiagnosed foetal malformation in around one in 300 women. The majority of anomalies detected were renal and many resolved on their own.

A population-based study included 15,244 women with singleton pregnancy attending antenatal care over a two-year period in Oxfordshire, UK.

3.1 per cent of foetuses had malformations. Of these, 21.7 per cent were detected prior to the anomaly scan, 36.7 per cent during the anomaly scan, 2.3 per cent after the anomaly scan and prior to the third-trimester scan, 9.1 per cent at the third-trimester scan and 30.2 per cent after birth. The likelihood of detecting a new malformation during a third-trimester scan was one in 303 (95% CI, 233-432) women.

The most common anomalies detected during the routine third-trimester scan were of the urinary tract (70%). The majority of these cases were of isolated renal pelvic dilatation, of which 57 per cent resolved spontaneously. Ventriculomegaly (12%) and simple ovarian cysts (9%) were the other common anomalies detected during the third-trimester scan.

Writing in the  American Journal of Obstetrics and Gynecology , the authors emphasise that the detection of congenital malformation during the third-trimester scan is incidental and that the scan has little effect on the overall detection rates. Nevertheless, they recommend that "this information should be available to women attending a third-trimester growth scan; to sonologists undertaking such screening; and should be taken into consideration of cost analysis when planning universal third-trimester ultrasound scanning."

Drukker L, Cavallaro A, Salim I, Ioannou C, Impey L, Papageorghiou AT. How often do we incidentally find a fetal abnormality at the routine third-trimester growth scan? A population-based study. Am. J. Obstet. Gynecol.2020 Jun 03 [Epub ahead of print]. doi: 10.1016/j.ajog.2020.05.052. PMID: 32504567.  Abstract.

This article originally appeared on Univadis, part of the Medscape Professional Network.

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