Geburtshilfe Frauenheilkd 2016; 76 - P39
DOI: 10.1055/s-0036-1583812

Prenatal screening for trisomy 21

J Diari 1, A Gharsa 1, A Achour 1, C Abid 1, D Chelli 1
  • 1Gynecology and obstetrics department A, Maternity Center Rabta, Tunis, Tunisia


Down syndrome is responsible of different anatomical malformations and mental retardation. A growingbody of evidence-based studies has demonstrated that fetal nuchal translucency can be a powerful prenatal screening tool and combined with first trimester serum markers, it can be incredibly promising in near future.


The aim of our study was to study the strategies of prenatal screening for trisomy 21 and evaluate its results.


Retrospective study conducted at the service A of the maternity and neonatology center of Tunis during a period of 10 years. We included all cases of trisomy 21 diagnosed prenatally, born alive or abortion products (33 cases). We searched screening methods used and we evaluated their performance.


In our study, the overall prevalence of trisomy 21 was 1.67 per 1000 pregnancies. Prenatal screening interested 46.47% of patients. The diagnosis of trisomy 21 was prenatally made in 84.84% of cases. 15.15% of patients escaped prenatal diagnosis. The mean maternal age was 36.14 years. The mean gestational age at diagnosis was 17 weeks. Ultrasound screening led to the diagnosis in 54.54% of cases with a sensitivity of 61.11%. Maternal serum markers (free fraction BHCG and PAPP-A) contributed to the diagnosis in 9.09% of cases with positive income in all cases. Those of the 2nd trimester (free fraction BHCG, AFP, unconjugated estriol) were achieved in 24.24% of cases, with a sensitivity of 75%. Second trimester ultrasound scan has detected 33% of foetuses with T21.


A diverse range of protocols and strategies have been reported in the published literature which can be applied in the detection of DS using the NT and a variety of serum markers during different stages of the gestation. The most effective sonographic maker of trisomy 21 and other chromosomal defects is increased NT at 11 – 14 weeks. The first trimester maternal serum screening has consistently revealed that pregnancies with fetal DS are associated with higher levels of total HCG and of the free HCG and lower levels of pregnancy-associated plasma protein A. The advantage of combination of nuchal translucency and first and second trimester serum markers stems from the fact that it can outline a very high sensitivity for DS as high as 94% for a 5%false-positive rate.


Prenatal screening for trisomy 21 is constantly improving. Ultrasound screening (especially that of the first trimester) is an important pillar in screening strategies.