Changes in fetal prevalence and outcome for trisomies 13 and 18: a population-based study over 23 years

Objective. Changes in prenatal diagnosis and maternal age are likely to have an impact on live born prevalence of trisomies 13 and 18. We investigated trends in diagnosis, prevalence, and survival in these conditions. Methods. A population-based study of one UK health region in 1985-2007 using a well-established congenital abnormality register. Individual records were reviewed and live birth and maternal age data obtained. Results. Pregnancies with trisomies 13 and 18 increased from 0.08 to 0.23 per 1000 registered births and 0.20 to 0.65 per 1000 registered births, respectively. Prenatal diagnosis increased and was associated with high termination rates. Live born prevalence with trisomy 13 decreased from 0.05 to 0.03 per 1000 live births and with trisomy 18 from 0.16 to 0.10 per 1000 live births. Postnatal survival remains poor: one baby (3%) with trisomy 13 and four (6%) with trisomy 18 survived the first year. The percentage of mothers over 35 years increased from 6 to 15%. Conclusions. Changes in prenatal screening and maternal age have had dramatic effects on the live born prevalence of trisomies 13 and 18. Infant survival remains largely unchanged with the majority dying in the neonatal period.