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Maternal age and gestation-specific risk for trisomy 21.
Snijders RJ, Sundberg K, Holzgreve W, Henry G, Nicolaides KH.
Ultrasound Obstet Gynecol 1999;13:167-70. -
Maternal serum S100 protein in normal and Down syndrome pregnancies.
Abraha HD, Noble PL, Nicolaides KH, Sherwood RA.
Prenat Diagn 1999;19:334-6.