Abstract

Trisomy 18 (T18) and trisomy 13 (T13) are the second and third most common autosomal aneuploidy syndromes; both are the result of an extra l8th or l3th chromosome, respectively, being present in each cell. T18 occurs in around 1 in 5000 births and T13 in around 1 in 10,000, but many pregnancies end under 24 weeks of pregnnancy and it is uncommon to continue to full term. We examined the natural history (including diagnosis, pregnancy outcome, pregnancy complications and infant survival) of T18 and T13 pregnancies in a setting where termination of pregnancy was not available and where anomaly ultrasound scanning was not routine. All identified T18 and T13 pregnancies from 2001 to 2012 were included; 46 and 24, respectively. Most T18 cases (65%) were diagnosed during pregnancy, compared to only one third of T13. Only three T18 pregnancies and one T13 pregnancy were electively terminated outside the jurisdiction. 48% (T18) and 46% (T13) infants survived following birth, for a median of 1.5 days (T18) and 7 days (T13). This study provides important information for professionals and women. These pregnancies can be undiagnosed during pregnancy without routine anomaly scanning. While many fetuses die before birth, postnatal survival is possible.