Further data suggesting that assessment of atypicality may be a valuable addition to Down's syndrome screening is presented, based on results from 1521 unaffected pregnancies and 190 chromosomally abnormal pregnancies. For a 1 % increase in false positive rates (over the Down's screening-related false positives), it is estimated that the detection of non-trisomy 21 abnormalities may be enhanced by approximately 40%. These false positive and detection rates are similar to previous reports for specific trisomy 18 screens. Further work is necessary to prove whether a specific trisomy 18 screen, or an atypicality screen is preferable.
WrightDReynoldsTDonovanC. Assessment of atypicality: An adjunct to prenatal screening for Down's syndrome that facilitates detection of other abnormalities. Ann Clin Biochem1993; 30: 578–83
2.
CrossleyJAitkenDBerryEConnorJ. Screening for trisomy 18: A practical addition to biochemical screening for Down's syndrome. In: Proceedings of the ACB National Meeting. 1995 May 15–19; Glasgow. London: RSM Press, 1995. A68
3.
PalomakiGHaddowJKnightGWaldNJKennardACanickJA. Risk-based prenatal screening for trisomy 18 using alpha-fetoprotein, unconjugated oestriol and human chorionic gonadotropin. Prenat Diagn1995; 15: 713–23
4.
SpencerKMallardACoombesEMacriJ. Prenatal screening for trisomy 18 with free β human chorionic gonadotrophin as a marker. BMJ1993; 307: 1455–8
5.
BogartMPandianMJonesO. Abnormal maternal serum chorionic gonadotropin levels in pregnancies with fetal chromosome abnormalities. Prenat Diagn1987; 7: 623–30
6.
JohnsonACowchockFDarbyMWapnerRJacksonL. First trimester maternal serum alpha-fetoprotein and chorionic gonadotropin in aneuploid pregnancies. Prenat Diagn1991; 11: 443–50
7.
StaplesARobertsonERanieriERyallRHaanE. A maternal screen for trisomy 18: An extension of maternal serum screening for Down's syndrome. Am J Hum Genet1991; 49: 1025–33
8.
BurtonBPrinsGVerpM. A prospective trial of prenatal screening for Down syndrome by means of maternal serum α-fetoprotein, human chorionic gonadotropin and unconjugated estriol. Am J Obstet Gynecol1993; 169: 526–30
9.
AitkenRKingJGeorgeP. Screening for Down's syndrome. Ann Clin Biochem1994; 31: 300–1
10.
WenstromKWilliamsonRGrantS. Detection of fetal Turner's syndrome with multiple marker screening. Am J Obstet Gynecol1994; 170: 570–3
11.
BennPHomeDBrigantiSGreensteinR. Prenatal diagnosis of diverse chromosome abnormalities in a population of patients identified by triple marker testing as screen positive for Down syndrome. Am J Obstet Gynecol1995; 173: 496–501
12.
WaldNCuckleHDensemJNanchahalKRoystonPChardT. Maternal serum screening for Down's syndrome in early pregnancy. BMJ1988; 297: 883–8
13.
BuchananPKrantzDKasturiRCookEMacriJ. Identification of trisomy 18, triploidy and other abnormalities: The use of an atypicality index incorporating maternal serum FreeBeta and AFP. Am J Hum Genet1994; 55: A277
