ACOG Practice Bulletin: Prenatal Diagnostic Testing for Genetic Disorders Number 162, May 2016. Replaces Number 88, December 2007.
ACOG Practice Bulletin: Screening for Fetal Aneuploidy, Number 163, May 2016. Replaces Number 77, January 2007.
Cunningham F, et al. Williams Obstetrics. 24th ed. The McGraw Hill Companies, Inc. 2014.
Lockwood, C. Guidelines for Perinatal Care. 7th ed. AAP and ACOG. 2012.