title: Down syndrome screening in multiple pregnancies.
abstract: First or second trimester screening in twin pregnancies is feasible and still efficacious by using either a combination of ultrasound and maternal serum biochemistry in the first trimester or maternal serum biochemistry in the second trimester. Special care, however, should be emphasized in what concerns biochemical screening, since it is much less sensitive in multiples. These "pseudo-risks" have been challenged for their scientific and clinical validity, however. Until more data are available from larger studies on the distribution of markers in concordant or discordant twins, nuchal translucency estimated for each fetus should be the predominant factor by which women who present with increased risk should be counseled regarding invasive testing. In dizygotic pregnancies, pregnancy-specific risk should be calculated by summing the individual risk estimates for each fetus. In monozygotic twins, the risk should be calculated based on the geometric mean of both nuchal translucency measurements, not forgetting that the false-positive rate of nuchal translucency screening is expectantly higher than in singletons.
authors.affiliation: Department of Obstetrics and Gynecology, Faculty of Medicine, Porto, University Hospital of S. João, Porto, Portugal. almatias@mail.telepac.pt
authors.forename: Alexandra
authors.initials: A
authors.lastname: Matias
authors.forename: Nuno
authors.initials: N
authors.lastname: Montenegro
authors.forename: Isaac
authors.initials: I
authors.lastname: Blickstein
mesh_terms: D015415:Biomarkers / Q000097:blood; D002823:Chorion; D004200:Diseases in Twins; D004314:Down Syndrome / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D005865:Gestational Age; D006801:Humans; D008403:Mass Screening; D009333:Neck / Q000000981:diagnostic imaging / Q000196:embryology; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011296:Prenatal Diagnosis / Q000379:methods*; D014427:Twins; D014430:Twins, Monozygotic; D016216:Ultrasonography, Prenatal
chemical_list: D015415:Biomarkers