[Screening of chromosome anomalies during the first trimester]

In view of today's knowledge, it is evident that a very efficient screening for chromosome anomalies can be carried out during the first trimester. Prospective studies of a total of 200,868 pregnancies-among them 871 fetuses with trisomy 21-have shown that measuring the nuchal transparency can identify 76.8% of fetuses with trisomy 21, with a false-positive rate of 4.2%. If the measurement of nuchal transparency is combined with that of the maternal serum concentrations of free human beta-choriogonadotropin and pregnancy-associated plasma A, the detection rate is 87.0% with a false-positive rate of 5% (prospective studies of altogether 44,630 pregnancies with 215 fetuses suffering from trisomy 21). At present, further signs of Down syndrome in the first trimester are being investigated, such as the missing fetal nasal bone, the maxilla and the blood flow pattern in the ductus venosus. Well-known signs of trisomy 13 and 18, which are already visible in the first trimester, are megacystis, omphalocele, polydactyly and holoprosencephaly. Most pregnant women prefer being screened during the first instead of the second trimester. Therefore every expectant mother should be offered an appropriate examination during the first trimester. It is essential for the effectiveness of the screening that the examiners be suitably trained and that the results of the ultrasound and laboratory examinations be subjected to a regular external quality control. In Austria, there is a general consent to follow the guidelines of the Fetal Medicine Foundation.