Trisomy 18 and 13 screening: consequences for the Dutch Down syndrome screening programme

Abstract

Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13) are the second and third most common autosomal trisomies after Down syndrome (trisomy 21). Most infants with a trisomy 18 or 13 die in utero and the others within the first year of life. Especially, in case of trisomy 13, there is an increased risk of severe and early onset pre-eclampsia (Boyd et al., 1987). To enable an early termination of trisomy 18 and 13 pregnancies, and to avoid maternal complications, screening for trisomy 18 and 13 seems a sensible option, especially since modelling has shown that current first trimester screening can detect both chromosomal anomalies with a high detection rate (DR) and low false positive rate (FPR) (Tul et al., 1999; Spencer et al., 2000). From January 2007 a governmentally approved national screening programme for Down syndrome has been implemented in the Netherlands, using the first trimester combined test [pregnancy-associated plasma protein A (PAPP-A), the free beta subunit of human choriongonadotrophin (fβ-hCG) and nuchal translucency (NT)]. The government license for this screening programme is strictly confined to screening for trisomy 21. Under the current license, it is not allowed to report on the risks for trisomy 18 and 13. However, since an increasing number of health care providers know the potential role of serum screening for trisomy 18 and 13, including some who already counsel their patient regarding these anomalies and since these trisomies are associated with early maternal complications it was recently decided to file a request to extend the government license to Edwards and Patau’s syndrome. This request is currently under review. The aim of this article is to predict the consequences for the Dutch screening programme in terms of DR and FPR if trisomy 18 and 13 screening is introduced, using an accepted algorithm and retrospective data of the Dutch programme.