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In a study published in Ultrasound in Obstetrics & Gynecology that involved more than 50,000 pregnancies, a fetal anomaly was detected for the first time in the third trimester in one in 200 women who had undergone a first and/or second trimester ultrasound examination.
Most of the fetal abnormalities (68%) seen at 35 to 37 weeks had already been diagnosed in the first and/or second trimester, and the incidence of abnormalities first seen at 35 and 37 weeks was 0.5%.
The study highlights the benefit of a late third trimester scan for detecting fetal abnormalities that were either missed in previous first and second trimester scans or became apparent only during the third trimester.