Objectives To determine the prenatal detection rate of abnormality (fetal anomaly or growth restriction) in pregnancies complicated by fetal trisomies 21, 18 and 13 in an obstetric population managed without routine biochemical or sonographic screening tests and to assess the perinatal outcome of these pregnancies.Subjects and methods This was a retrospective analysis of obstetric and neonatal data pertaining to infants born with trisomy 21, 18 or 13 (n=82) diagnosed between 1989 and 1997 (23 762 deliveries).Results Antenatal suspicion of aneuploidy, based on the detection of growth restriction or fetal anomaly, was present in 18.3% (11 of 60) of fetuses with trisomy 21, in 81.2% (13 of 16) of fetuses with trisomy 18, and in 83.3% (five of six) of fetuses with trisomy 13. The antenatal detection rates for growth restriction were accurate whereas the antenatal detection rates for fetal anomalies were poor. Intrauterine fetal death occurred in 18.8% of fetuses with, trisomy 18 (three of 16) and in 50% (three of six) of cases of trisomy 13. For babies born alive with, trisomy 18 or 13 the neonatal mortality was 93.8% (15 of 16). All cases of trisomy 21 fetuses survived beyond the perinatal period and the antepartum and intrapartum details of these pregnancies were unremarkable.Conclusion In obstetric practice without routine biochemical or sonographic screening tests the detection of findings suggestive of aneuploidy is low for trisomy 2 1, but is high for trisomies 18 and 13. These findings provide information for counseling about the antenatal, intrapartum, and neonatal course of these trisomies.