Risicoschatting voor Down syndroom/neuraalbuisdefecten door analyse van triple test parameters in maternaal serum 1995-1999

Between 1995 and 1999 the RIVM processed about 16,000 triple tests to estimate risks for the Down syndrome and neural tube defect pregnancies. This research was carried out on order of the Health Care Inspectorate of the Dutch Ministry of Health, Welfare, and Sport. The survey described here investigated over 16,000 triple test requests from all the provinces in the Netherlands except Groningen, Friesland and Drenthe . Pregnancies were classified as either normal singleton pregnancies or special (e.g. diabetic, twin) pregnancies. Experimental data of the triple test (alpha fetoprotein, unconjugated oestriol and human chorionic gonadotropin hormone) for singleton normal pregnancies are given, with special reference to the age distribution of the population under investigation. The median values of the triple test parameters in Downs syndrome or neural tube defect-pregnancies are given, using reported data on the outcome of pregnancies, as well as the detection rate and false positive rate of the triple test. The practical and logistic implications of the triple test are discussed. A maximum was reached in 1996 of about 4000 triple test requests, with a stabilisation of around 3200 in the succeeding years. A decline in the number of requests from the university hospitals was accompanied by a rise in the number of applications from, in particular, peripheral hospitals. Between 1995 and 1999 an apparent rise from 34.1 to 35.1 years was observed in the median age of pregnant women requesting a triple test. This was accompanied by an elevation in the percentage of Down syndrome 'high risk' triple test results from 11.8 to 15.7%. Multiples of the median values for the triple test parameters were, with few exceptions, within the demands (log-normality, amount of bias) of the triple test risk estimation. A report of the outcome of the pregnancy was received for 70% of all the triple tests. Based on these data, the detection rate for Down syndrome was 89% for a 13.7% false positive rate, while the detection rate for neural tube defects was 63% for a 3.3% false positive rate. These specifications are in agreement with or exceed minimum values for detection and false positive rates, as estimated from the age distribution of the pregnant women