First trimester ultrasonographic detection of fetal aneuploidies and fetal structural abnormalities in an unselected population

ABSTRACT

To determine the value of early pregnancy ultrasonography in detecting fetal structural and chromosomal abnormalities in an unselected obstetric population. Prospective, observational, cross-sectional, screening study. Al-Azhar University Hospitals in Damietta and Cairo. 1500 sequential unselected women [mean maternal age 28.3 years, range 18-42; mean gestational age 12 +4 weeks, range 11-14], carrying 1468 live fetuses participated in this study. All women initially underwent transabdominal ultrasonograpy and when the anatomical survey was considered to be incomplete, transvaginal ultrasonography was also performed [20.1%]. Nuchal translucency was measured and karyotyping was performed as appropriate. Detection rate of fetal anomalies and measurements of nuchal translucency thickness. Pregnancy outcome was obtained through karyotyping, outcome questionnaires and examination of the newborn infants. The incidence of anomalous fetuses was 1.4% [21/1468] including 9 chromosomal abnormalities. The detection rate for structural abnormalities was 62.5% [10/16] and the specificity was 99.9% in early pregnancy. When the first and second trimester scans were combined, the detection for structural abnormalities was 81% [13/16]. Hundred percent [9/9] of chromosomal abnormalities were diagnosed at 11-14 weeks, either because of a nuchal translucency greater than or equal to the 99 th centile for gestational age [66.6%; 6/9] or due to the presence of structural abnormalities [44%; 3/9]. Hundred percent [6/6] of cases of trisomy 21 were also diagnosed either because of having a nuchal translucency >/= 99 th centile [67%; 4/6] or due to the presence of a structural abnormality [33%; 2/6]. It was found that a cut-off point >/= 3 for fetal nuchal translucency could predict trisomies 21 and 18 with a sensitivity 67 and 50%, specificity 96.6 and 96.6%, positive predictive value 7.5 and 2% and negative predictive value 99.8 and 99.9%, respectively. A significant proportion of fetal structural and chromosomal abnormalities can be detected by ultrasonographic screening at 11-14 weeks, but the second trimester scan should not be abandoned. The sensitivity of detection can be improved by combining measurement of nuchal translucency with detailed examination of fetal anatomy