First trimester ultrasonographic diagnosis of fetal structural abnormalities in a low risk population

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Abstract
Objectives Ultrasonographic screening between 12+01 and 13+6 weeks for fetal structural abnormalities using transab dominal sonography and, where necessary, transvaginal sonography in a low risk population. Design A prospective observational study Setting London teaching hospital Methods Pregnant women with a total of 1632 low risk viable fetuses between 12+0 and 13+6 weeks of gestation were scanned using transabdominal and, where necessary, transvaginal sonography (40%). If the anatomical survey was normal, the women underwent routine 18‐20 week anomaly scans. Pregnancy outcomes were obtained from radiological and neonatal computerised databases, and postal or telephone patient enquiry. Results Seventeen (1.0%) major structural abnormalities were diagnosed in the study group. Of these, 11 (64.7%) were diagnosed at the 12‐13 week scan, three diagnosed in the mid‐trimester and three postnatally. Of the fetal abnormalities diagnosed antenatally, 78.6% were diagnosed in the first trimester. The sensitivity of abnormality detection by the combination of both first and second trimester scans was 82.3%. In addition, a significant number of missed abortions (n= 36) were also diagnosed by the first trimester scan. Conclusion This study has demonstrated the potential of screening a low risk population for fetal abnormalities at 12‐13 weeks of gestation using transabdominal sonography and, where necessary, transvaginal sonography. Larger studies are required to establish the clinical value of the first trimester scan.