One‐stop clinic for assessment of risk for trisomy 21 at 11–14 weeks: a prospective study of 15 030 pregnancies

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Abstract
Objective: To evaluate the performance of a one‐stop clinic for assessment of risk (OSCAR) for trisomy 21 by a combination of maternal age, fetal nuchal translucency (NT) thickness and maternal serum free β‐human chorionic gonadotropin (hCG) and pregnancy‐associated plasma protein‐A (PAPP‐A) at 11–14 weeks of gestation.Method: Screening for trisomy 21 was carried out by OSCAR in 15 030 singleton pregnancies with live fetuses at 11–14 weeks. The estimated risk for trisomy 21 was calculated, and the women were counseled regarding this risk and the option of invasive testing or expectant management. Follow‐up of the outcome of all pregnancies was carried out. The detection and false‐positive rates for different risk cut‐offs were calculated.Results: Fetal NT and maternal serum free β‐hCG and PAPP‐A were successfully measured in all cases. Pregnancy outcome, including karyotype results or the birth of a phenotypically normal baby, was obtained from 14 383 cases. The median maternal age of these cases was 34 (range 15–49) years and in 6768 (47.1%) the age was 35 years or greater. The median gestation at screening was 12 (range 11–14) weeks and the median fetal crown–rump length was 64 (range 45–84) mm. The estimated risk for trisomy 21 based on maternal age, fetal NT and maternal serum free β‐hCG and PAPP‐A was 1 in 300 or greater in 6.8% (967 of 14 240) normal pregnancies, in 91.5% (75 of 82) of those with trisomy 21 and in 88.5% (54 of 61) of those with other chromosomal defects. For a fixed false‐positive rate of 5% the respective detection rates of screening for trisomy 21 by maternal age alone, maternal age and serum free β‐hCG and PAPP‐A, maternal age and fetal NT, and by maternal age, fetal NT and maternal serum biochemistry were 30.5%, 59.8%, 79.3% and 90.2%, respectively.Conclusion: Screening for trisomy 21 by a combination of maternal age, fetal NT and maternal serum biochemistry at 11–14 weeks can be provided in an OSCAR setting and is associated with a detection rate of about 90% for a false‐positive rate of 5%. Copyright © 2002 International Society of Ultrasound in Obstetrics and Gynecology

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