Objective To evaluate the natural fetal and neonatal outcome for pregnancies with an established prenatal diagnosis of fetal trisomy 18, and a parental decision for continuation of the pregnancy.Methods The obstetric and neonatal outcome data for 23 such pregnancies, diagnosed at a single referral Fetal Medicine Centre, were retrospectively obtained.Results The overall intrauterine fetal death rate was 61%, with a progressive decline in live fetuses up to 39 weeks gestation. For fetuses diagnosed before 20 weeks gestation, there was a trend towards a higher intrauterine fetal death rate (88%), in comparison to those diagnosed after this period (44%) (p=0.06). For live births, the preterm delivery rate was 44%. All infants born alive died within 48 h of birth.Conclusion These data provide reliable information for parental counselling pertaining to risk of intrauterine death when trisomy 18 is diagnosed prenatally. These findings suggest that long-term survival implications for trisomy 18 are different when it is diagnosed prenatally. included cases of trisomy 18 diagnosed either prenatally or postnatally, reported a total intrauterine fetal death rate of 45%, between 28 and 41 weeks gestation, and hence a live birth rate of 55%, for those diagnosed prenatally.(6) There is a clear need for more studies analysing natural outcome after prenatal diagnosis of trisomy 18 in utero.(5) The aim of this study was to evaluate the fetal and neonatal outcome for all pregnancies for which there was a prenatal diagnosis of trisomy 18, and a parental decision for continuation of the pregnancy.