Prospective evaluation of a first trimester screening program for Down syndrome and other chromosomal abnormalities using maternal age, nuchal translucency and biochemistry in an Australian population

Background: A combination of maternal age and ultrasound assessment of the nuchal translucency (NT) has been used in the first trimester to screen for chromosomal abnormality. In the United Kingdom, the addition of NT screening was shown to be beneficial. Aims: To report the sensitivity of combined first trimester biochemistry and ultrasound screening for Down syndrome in an Australian private practice specialising in obstetric ultrasound. Methods: A prospective study in a private obstetric ultrasound practice. Over 22 months, 2121 patients were screened and data was analysed for sensitivity (detection) and false positive rates for all chromosome abnormalities. Results: There were 17 chromosomal abnormalities, five of which were Down syndrome. Using maternal age alone or age and biochemistry, four of the Down syndrome cases were detected for a 29 and 19% false positive rate, respectively. Using age and NT or age, NT and biochemistry, all the Down syndrome cases were detected, for a false positive rate of 5.7 and 7.2%, respectively. The difference in detection rates for Down syndrome or other chromosomal abnormalities, using the four screening methods, did not reach statistical significance. However, the false positive rates in screening methods without ultrasound to assess the NT was significantly higher (P < 0.01). Conclusions: A combination of maternal age, NT and maternal serum biochemistry gives a high detection rate for both trisomy 21 and other chromosomal abnormalities. Down syndrome screening using either maternal age alone or age in combination with first trimester biochemistry conferred screen positive rates significantly higher than when combined with NT.