There are currently limited data describing the natural history and outcome for fetal trisomy 13 diagnosed prenatally. The aim of this study was to evaluate the fetal and neonatal outcome for pregnancies with an established prenatal diagnosis of fetal trisomy 13, and a parental decision for continuation of the pregnancy. To this end, the obstetric and neonatal outcome data for such pregnancies, diagnosed at two referral Fetal Medicine Centers, were retrospectively obtained and examined. During the study period, there were 45 cases of trisomy 13 diagnosed at both units, of which 26 (56%) continued with the pregnancy to its natural outcome. There were 12 intrauterine deaths in the cohort resulting in a rate of 46.2% of intrauterine lethality. Conversely, the live birth rate was 53.8%. For infants born alive, neonatal death on day 1 of life occurred in 78.6% of cases. The overall early neonatal mortality rate was 93%. There was one infant death at 6 weeks of age and no survival noted beyond this period. These data provide reliable information for parental counseling pertaining to risk of intrauterine death when trisomy 13 is diagnosed prenatally. These data also indicate that the survival outcome is worse than that previously accepted from studies of postnatal follow up of live born infants with this diagnosis. (C) 2014 Wiley Periodicals, Inc.