Antenatal maternal serum screening for Down's syndrome: results of a demonstration project.
OBJECTIVE
To assess the implementation of antenatal screening for Down's syndrome in practice, using individual risk estimates based on maternal age and the three serum markers: alpha fetoprotein, unconjugated oestriol, and human chorionic gonadotrophin.


METHODS
Demonstration project of Down's syndrome screening; women with a risk estimate at term of 1 in 250 or greater were classified as "screen positive" and offered diagnostic amniocentesis.


METHODS
Hospital and community antenatal clinics in four health districts in London.


METHODS
12,603 women of all ages with singleton pregnancies seen between February 1989 and the end of May 1991, with follow up of the outcome of pregnancy completed to the end of 1991.


METHODS
Uptake of screening, detection rate for Down's syndrome, false positive rate, odds of being affected given a positive result, and uptake of amniocentesis in women with positive screening results, together with the costs of the screening programme.


RESULTS
The uptake of screening was 74%. The detection rate was 48% (12/25), and the false positive rate was 4.1%, consistent with results expected from previous work based on observational studies. There was a loss of detection due to the selective use of ultrasound scans among women with positive screening results. One affected pregnancy occurred among 205 reclassified as negative; this illustrated the danger of false negatives occurring in this group and lends weight to the view that if an ultrasound estimate of gestational age is used it should be carried out routinely on all women rather than selectively among those with positive results. The estimated cost of avoiding the birth of a baby with Down's syndrome was about 38,000 pounds, substantially less than the lifetime costs of care.


CONCLUSIONS
Antenatal maternal serum screening for Down's syndrome is effective in practice and can be readily integrated into routine antenatal care. It is cost effective and performs better than selection for amniocentesis on the basis of maternal age alone.
Wald
N J
NJ
Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, Medical College of St Bartholomew's Hospital, London.
Kennard
A
A
Densem
J W
JW
Cuckle
H S
HS
Chard
T
T
Butler
L
L
D000649:Amniocentesis; D006063:Chorionic Gonadotropin / Q000097:blood; D004314:Down Syndrome / Q000175:diagnosis*; D004964:Estriol / Q000097:blood; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D005315:Fetal Diseases / Q000175:diagnosis*; D006801:Humans; D011247:Pregnancy; D011296:Prenatal Diagnosis / Q000379:methods*; D012307:Risk Factors; D000509:alpha-Fetoproteins / Q000032:analysis
D006063:Chorionic Gonadotropin; D000509:alpha-Fetoproteins; D004964:Estriol