Increased first trimester nuchal translucency: pregnancy and infant outcomes after routine screening for Down's syndrome in an unselected antenatal population

Although increased nuchal translucency (NT) has been linked to a wide range of fetal chromosomal abnormalities and genetic syndromes, very few studies have looked at the outcomes of chromosomally normal pregnancies in unselected obstetric populations. This study aims to evaluate the outcomes of pregnancies with nuchal translucency measurements greater than or equal to 4 mm in a low risk obstetric population attending for routine first trimester screening. Women attending for booking scans were routinely offered nuchal translucency measurement as a screening test for Down's syndrome between 10 and 14 weeks gestation. The prevalence of increased nuchal translucency was 0.8% (n=53). There were 15 (28.3%) chromosomal abnormalities, the commonest of which was Down's syndrome. Of the 38 chromosomally normal pregnancies, seven resulted in intrauterine death, early neonatal death or termination of pregnancy. The remaining 31 cases resulted in livebirths, of which two infants now exhibit developmental delay of unknown aetiology and one has been diagnosed as having Noonan's syndrome. 10 (19%) pregnancies were diagnosed as having major anatomical malformations resulting in fetal or neonatal demise or requiring postnatal surgery. In a routine obstetric population, the finding of an NT measurement greater than or equal to 4 mm is associated with a poor pregnancy outcome in the majority of cases, mainly owing to chromosomal abnormality. This study establishes the need for focused fetal assessment in cases with such first trimester findings.