Objectives: To establish the best timing for the realization of first-trimester-morphologic-evaluation, following routine midtrimester fetal-ultrasound-scan-recommendations (RFUSR), by performing exclusive transabdominal exploration, and to determine the sensitivity of the mentioned scan for diagnosis of major structural abnormalities.Method: Prospective observational study with 512 pregnant women with singleton gestations (438 low-risk, 74 high-risk) was conducted. Early fetal morphological evaluation (EFME) is performed in line with RFUSR (18-22 weeks) (ISUOG 2010) and a check-list structured evaluation was followed, between 11-13 + 6 weeks. Its performance is assessed in the correct identification of normal fetal anatomy, and its effectiveness in the detection of structural defectsResults: Five hundred and four pregnant women were evaluated, of which, 58.3% EFME are considered complete fetal anatomical surveys. Complete fetal anatomical surveys scans rise from 23.1% at 11-11 + 6 weeks to 63.8% at 13 + 3-13 weeks, with a clear turning point at 12 + 6-13 + 3 weeks (63.8%) (p < .05). From 12 + 6-13 + 3 weeks only renal (26.3%) and cardiac assessments (31.6%) present an inconclusive evaluation greater than 20%. Body mass index (23.9 versus 29.8) and estimated fetal weight (63 versus 86.7 g) influence EMFE's ability of identifying fetal structures (p < .05). EMFE presents sensitivity for the identification of structural malformations of 83.3% (20/24).Conclusions: From 12 + 6 weeks of gestation onwards, a complete fetal morphological evaluation can be performed in 63.8% of cases following the routine midtrimester fetal ultrasound scan recommendations (ISUOG's 20 weeks scan).
Keywords: Anatomy ultrasound; fetal anomalies; first-trimester; ultrasound scan.