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Objective To evaluate the performance of a one-stop multidisciplinary clinic of screening for fetal chromosomal anomalies in the first trimester of pregnancy by a combination of maternal serum biochemistry and ultrasonography.

Design Retrospective review of screening performance.

Setting District General Hospital maternity unit.

Population All women booked for routine antenatal care at Harold Wood Hospital between 1 June 1998 and 31 May 2001. The population included 12,339 women with singleton pregnancies presenting at 10–14 weeks of gestation.

Methods Women were offered screening using a combination of maternal serum free β-hCG and pregnancy associated plasma protein-A (PAPP-A) and fetal nuchal translucency thickness. Those with an estimated risk of ≥1 in 300 of carrying a fetus with trisomy 21 or trisomy 18 or trisomy 13 were offered the option of an invasive diagnostic test. Follow up of the outcome of all pregnancies was carried out.

Main outcome measures Uptake of screening and invasive testing, detection rate for fetal chromosomal abnormalities and false positive rate.

Results The uptake of first trimester screening was 97.5% and the uptake of invasive testing in the increased risk group was 77%. The rate of detection of trisomy 21 was 92% (23 of 25), of trisomy 13 or 18 was 100% (all 15) and of all aneuploidies was 96% (49 of 51). The false positive rate was 5.2%.

Conclusion First trimester screening for trisomy 21 and other aneuploidies can be delivered in an efficient manner in a one-stop multidisciplinary clinic. The detection rates are far better than can be achieved by second trimester serum screening.