Staples, A. J., Robertson, E. F., Ranieri, E., Ryall, R. G., & Haan, E. A. (1991). A maternal serum screen for trisomy 18: An extension of maternal serum screening for Down syndrome.

Staples, A J., E F. Robertson, E. Ranieri, R G. Ryall, και E A. Haan. A Maternal Serum Screen for Trisomy 18: An Extension of Maternal Serum Screening for Down Syndrome. 1991.

Staples, A J., et al. A Maternal Serum Screen for Trisomy 18: An Extension of Maternal Serum Screening for Down Syndrome. 1991.