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There are significant correlations between biochemical markers but not NT in successive pregnancies, leading to increased risk of recurrence of FP results. However, such increase is not statistically significant if the overall FP rate is very low.

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Background. Screenitig strategies for the detccrion of aneuploidies should be performed by every Prenatal Diagnosis Ser\'ice. Several screening approaches have been developed, reaching detection rates of at least 85% for a 5% false-positive rate. Our experience in a population with a high percent of women aged 35 or older using combined screening is presented. Methods. From July 1999 to October 2004, we conducted a prospective study of screening for fetal aneuploidies among pregnant women between 10 and 14 weeks. Risks for aneuploidy were calculated by combined screening, using maternal age, maternal serum free-/JhCG, pregnancy-associated plasma protein-A (PAPP-A) and fetal nuchal translucency. The result was considered positive if the combined risk exceeded the cut off risk of 1/270. Results. Screening was completed in 4538 singleton pregnancies. The mean maternal age was 31.08 years, and in 25.9% the age was 35 years or greater. The detection rate was 76.9% (30/39) for all aneuploidies with a false-positive rate of 3,6%. For trisomy 21, the detection rate was I'i.l'Vu (14/19) with a false-positive rate of 3.6%. At a 5% false-positive rate, the sensitivity of combined screening and nuchal translucency were 78.9% and 63.2% respectively. Conclusiom. First trimester combined screening is efficient, and its application can be assumed in a tertiary-hospital.