Trisomy 13, trisomy 18, and triploidy belong to the chromosomal abnormalities which are compatible with life, but which are also associated with a high rate of spontaneous abortion, intrauterine death, and a short life span. This study was conducted to analyze natural outcome after prenatal diagnosis of these disorders. Between January 1, 1999 and December 31, 2009, we investigated all amniocenteses and chorionic villus biopsies carried out at our department. All cases with fetal diagnosis of triploidy, trisomy 13, and 18 were analyzed, with a focus on cases with natural outcome. Overall, 83 (78%) cases of pregnancy termination and 24 (22%) patients with natural outcome (NO) were identified. The NO group included 15 cases of trisomy 18, six cases of triploidy, and three cases of trisomy 13. No case of triploidy was born alive. The live birth rate was 13% for trisomy 18 and 33% for trisomy 13. The three live-born infants with trisomy 13 and 18 died early after a maximum of 87 hr postpartum. Our data are consistent with the literature concerning outcome of triploidy, with none or only a few live births. Analyzes of trisomy 13 and 18 indicate a very short postnatal life span. Different study designs and diverse treatment strategies greatly affect the fetal and neonatal outcome of fetuses with triploidy, trisomy 13, and 18. More studies analyzing natural outcome after prenatal diagnosis of these chromosomal abnormalities are needed. Non-termination of these pregnancies remains an option, and specialists advising parents need accurate data for counseling. © 2011 Wiley Periodicals, Inc.