How often do we identify fetal abnormalities during routine third-trimester ultrasound? A systematic review and meta-analysis.

BACKGROUND: Routine third-trimester ultrasound is frequently offered to pregnant women to identify fetuses with abnormal growth. Infrequently, a congenital anomaly is incidentally detected. OBJECTIVE: To establish the prevalence and type of fetal anomalies detected during routine third-trimester scans using a systematic review and meta-analysis. SEARCH STRATEGY: Electronic databases (MEDLINE, Embase and the Cochrane library) from inception until August 2019. SELECTION CRITERIA: Population-based studies (randomised control trials, prospective and retrospective cohorts) reporting abnormalities detected at the routine third-trimester ultrasound performed in unselected populations with prior screening. Case reports, case series, case-control studies and reviews without original data were excluded. DATA COLLECTION AND ANALYSIS: Prevalence and type of anomalies detected in the third trimester. We calculated pooled prevalence as the number of anomalies per 1000 scans with 95% confidence intervals. Publication bias was assessed. MAIN RESULTS: The literature search identified 9594 citations: 13 studies were eligible representing 141 717 women; 643 were diagnosed with an unexpected abnormality. The pooled prevalence of a new abnormality diagnosed was 3.68 per 1000 women scanned (95% CI 2.72-4.78). The largest groups of abnormalities were urogenital (55%), central nervous system abnormalities (18%) and cardiac abnormalities (14%). CONCLUSION: Combining data from 13 studies and over 140 000 women, we show that during routine third-trimester ultrasound, an incidental fetal anomaly will be found in about 1 in 300 scanned women. This information should be taken into account when taking consent from women for third-trimester ultrasound and when designing and assessing cost of third-trimester ultrasound screening programmes. TWEETABLE ABSTRACT: One in 300 women attending a third-trimester scan will have a finding of a fetal abnormality.