OBJECTIVES: To assess the detection rate of triploidy at first-trimester screening for trisomy 21 and evaluate outcome in triploid pregnancies. METHODS: From 2008-2011, 198,427 patients women with singleton pregnancies underwent first-trimester screening (FTS) at 11+2 - 14+0 weeks of gestation. FTS included: Nuchal translucency (NT), maternal serum free β-human chorionic gonadotrophin (β-hCG) and pregnancy associated plasma protein-A (PAPP-A). In all triploid fetuses FTS parameters were re-evaluated. Karyotypes were established by invasive testing (CVS or AC) or post abortem and obtained from the Danish Cytogenetic Central Register and the Danish Fetal Medicine Database. RESULTS: A total of 30 triploid fetuses attended FTS. Twenty-five triploid fetuses were diagnosed as a result of abnormal FTS, a detection rate of 83%.Twenty-three fetuses were identified due to a high risk of trisomy 13, 18 or 21 and two fetuses due to structural abnormalities at FTS. The incidence of triploidy at FTS was 1:6614. A smaller CRL than estimated by last menstrual period was found in 95 % of the fetuses with the data available for evaluation. Eight fetuses had larger BPD than expected by gestational age. 69, XXX fetuses had significantly lower β-hCG MoM and PAPP-A MoM than 69, XXY fetuses (p=0.045 and p=0.02). No infants with triploidy were born in the study period. Among the triploid gestations, 80% of the women chose termination of pregnancy, 16 % had spontaneous miscarriages, and one was stillborn. CONCLUSION: First trimester screening for trisomy 21 also provides a high detection rate for triploidy.