5David A,Krantz BS,John WL et al.Firsttrimester Down syndrome screening:Freeβ-human chorionic gonadotropir and pregnancy-assoaciated plasma protein A. American Journal of Obstetrics and Gynecology . 1996
6Seller MJ.Alphafetoprotein in midtrimesterDown’s syndrome fetal serum. Journal of Medical Genetics . 1990
7Cameron B,Saunders DM,Sinosich MJ.Isthere a rote for PAPP-A in antenatal screeningat midgestation. Placenta . 1994
8Merkatz JR,Nitowsky HM,Macri JN et al.Anassociation between low maternal serum α-fetoprotein and fetal chromosomal abnormalities. American Journal of Obstetrics and Gynecology . 1984
9Van Lith JMM.First-trimester maternal serumalpha-fetoprotein as a marker for fetal chromosomal disorders. Prenatal Diagnosis . 1994
10Muller F,Aegerter P& Bou EA.Prospectivematernal serum human chorionic gonadotropinscreening for the risk of fetal chromosomeanomalies and of subsequent fetal and neonataldeath. Prenatal Diagnosis . 1993
