One stop clinic for assessment of risk for fetal anomalies: a report of the first year of prospective screening for chromosomal anomalies in the first trimester

Objective To evaluate the introduction of a one stop multidisciplinary clin ic for screening for fetal chromosomal abnormalities in the first trimester by a combination of maternal serum biochemistry and ultrasonography provid ing a risk of chromosomal abnormalities within a one hour clinic visit. Design One year retrospective review of screening performance. Population All women attending for routine antenatal care. The population i ncluded 4190 singleton pregnancies in women of all ages screened between 10 weeks and 3 days and 13 weeks and 6 days of gestation between the periods 1 June 1998 and 31 May 1999 in a district general hospital antenatal clinic . Methods All women booked into the clinic were offered screening by a combin ation of maternal serum free beta human chorionic gonadotrophin (hCG) and p regnancy associated plasma protein A (PAPP-A) and fetal nuchal translucency thickness. Women at increased risk of carrying a fetus with trisomy 21 or trisomy 18/13 (greater than or equal to 1 in 300 at sampling) were offered counselling and an invasive diagnostic procedure. Follow up of the outcome of all pregnancies was carried out. Main outcome measures The detection rate for trisomy 21, trisomy 18/13 and all aneuploides, false positive rate, uptake of screening, uptake of chorio nic villus sampling in women identified at increased risk and fetal loss af ter chorionic villus sampling. Results Overall 97.6% of the women (4088/4190) accepted first trimester scr eening. The rate of detection of trisomy 21 was 86% (6/7), for trisomy 18/1 3 100% (9/9) and for all aneuploides 95% (18/19). Fetal death at presentati on was found in 1.6% of pregnancies (69/4088). Of women who accepted screen ing, 6.1% (257/4088) presented too late for fetal nuchal translucency measu rement and 6.5% of the women (271/4088) presented too early. The false posi tive rate was 6.7% (253/3762). Uptake of invasive testing was 83% (207/253) . Conclusion First trimester prenatal screening for chromosomal abnormalities using a combination of maternal serum biochemistry and fetal nuchal transl ucency thickness can achieve detection rates in excess of 90%. These servic es can be provided in a one stop multidisciplinary clinic.