The first trimester ‘combined test’ for the detection of Down syndrome pregnancies in 4939 unselected pregnancies

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Abstract
The high detection rate (DR) for Down syndrome (DS) pregnancies which can be achieved by measuring fetal nuchal translucency (NT) early in pregnancy can be improved by combining it with placental hormones [pregnancy‐associated plasma protein A (PAPP‐A) and free β‐human chorionic gonadotrophin (fβ‐hCG)] and maternal age (‘combined test’). In this study we wanted to assess the DR using the ‘combined test’ in an unselected population of self‐referred pregnant women at a false‐positive rate (FPR) of about 5%. NT, PAPP‐A, fβ‐hCG and maternal age were measured in all women with singleton pregnancies who booked for delivery in our hospital from 1 December 1997 to 31 April 2000 and who were between 10 and 13 completed weeks of gestation [crown–rump length (CRL) 35–70 mm]. The specific DS risk was calculated using the computer program Alpha Version 5aa (Logical Medical Systems, London, UK). A total of 4939 women were tested. Out of 14 DS pregnancies that occurred during this period of time, 12 were detected with the test. A total of 246 women had a false‐positive test result in a non‐DS pregnancy (FPR 5.0%). This makes the ‘combined test’ by far the best test for the detection of DS pregnancies in a low‐risk population. The constant increase in maternal age at the time of delivery can also lead to an improved DR if a simple age‐dependant protocol for DS detection is used, but only at the price of a much higher number of amniocenteses and subsequent abortions. The DR for DS can be increased much more markedly using the ‘combined test’ with a FPR that still remains at the level as it was in the early 1970s. Copyright © 2002 John Wiley & Sons, Ltd.