Nuchal translucency audit: low uptake of invasive testing in screen positive cases.

The association between first trimester increased nuchal translucency (NT) and aneuploidies has been well established. To date, screening in this country has been carried out on an 'ad hoc' basis, as there is no national screening programme. It occurs mainly on maternal request indicated by age or a past history of a trisomy. As an isolated test we audited 316 patients attending the NMH for nuchal translucency screening to assess the accuracy of the test. Over two years 316 patients were seen and counselled. Forty-four cases (13%) were screen positive (risk of Trisomy 21 > 1 in 300). One third (15 cases) of this group went on to have invasive testing, one third of which (5 cases) were diagnosed with a trisomy and two thirds (10 cases) had normal fetuses. The remaining twenty-nine women with a high-risk ratio declined invasive testing with risk ratios that ranged from 1 in 250 to 296. In those who were screen negative there were no cases of trisomies. In conclusion, NT screening in this review had a sensitivity of 100%. In spite of being screen positive two thirds of patients declined invasive testing.