Ultrasound detection of suspected chromosome abnormalities in the 1st and 2nd trimester. Results of a prospective study

4053 pregnancies were studied prospectively during 4 years (July 1988 to June 1992) with regard to the sonographical recognition of indications of chromosomal anomalies from 9 to 24 weeks, irrespective of the mother's age. The morphology of the fetal organs, the phenotype, the proportions of the fetal body, biometrical data and disorders of the placenta and the amniotic fluid were scrutinised. For the prediction of a chromosomal anomaly, a high sensitivity of 86.3% and specificity of 99.8% were found; the prevalence was 1.8%. The thickening of the nuchal fold or a nuchal oedema was the most significant fetal stigma and a guiding symptom in Turner's syndrome and in trisomy 21 and 18. When suspicious facts were found during ultrasonography, karyotyping was proposed after detailed counselling, especially to mothers below the age of 35. The extended sonographical examination is considered a non-invasive tool to differentiate the statistical age related risk of a chromosomal anomaly in each individual case.