title: Maternal serum free alpha-human chorionic gonadotrophin levels in twin pregnancies: implications for screening for Down's syndrome.
abstract: Maternal serum free alpha-human chorionic gonadotrophin (free alpha-hCG) levels were determined in twin and singleton pregnancies at 15-22 weeks of gestation using a set of stored serum samples relating to 200 twin pregnancies and 600 singleton control pregnancies matched for gestational age and duration of storage. Free alpha-hCG values are, on average, 1.66 times greater in twin pregnancies than in singleton pregnancies (95 per cent confidence interval 1.56-1.76). If maternal serum free alpha-hCG is used in screening for Down's syndrome, values in twin pregnancies can be adjusted using this result so that screening can be performed in twin pregnancies as well as in singleton pregnancies.
authors.affiliation: Department of Environmental and Preventive Medicine, Wolfson Institute of Preventive Medicine, St Bartholomew's Hospital Medical College, London, U.K.
authors.forename: N J
authors.initials: NJ
authors.lastname: Wald
authors.forename: J W
authors.initials: JW
authors.lastname: Densem
mesh_terms: D006063:Chorionic Gonadotropin / Q000097:blood*; D018997:Chorionic Gonadotropin, beta Subunit, Human; D004314:Down Syndrome / Q000097:blood* / Q000175:diagnosis; D004964:Estriol / Q000097:blood; D005260:Female; D005865:Gestational Age; D006801:Humans; D010446:Peptide Fragments / Q000097:blood*; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000097:blood*; D011296:Prenatal Diagnosis; D012016:Reference Values; D014427:Twins; D000509:alpha-Fetoproteins / Q000032:analysis
chemical_list: D006063:Chorionic Gonadotropin; D018997:Chorionic Gonadotropin, beta Subunit, Human; D010446:Peptide Fragments; D000509:alpha-Fetoproteins; D004964:Estriol