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.