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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 (randomized 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 1,000 scans with 95% confidence intervals (95% CI). Publication bias was assessed. MAIN RESULTS: The literature search identified 9,594 citations; thirteen 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 1,000 (95% CI 2.72 - 4.78) women scanned. 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 consenting women for third trimester ultrasound; and when designing and assessing cost of third trimester ultrasound screening programs.

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anomaly scan, congenital malformation, fetal abnormality, fetal anomaly, incidental finding, pregnancy care, systematic review, third-trimester