Bennett, S.; Cullen, J.; Sherer, D.; Woods Jr, J. (2008). "The Ferning and Nitrazine Tests of Amniotic Fluid Between 12 and 41 Weeks Gestation". American Journal of Perinatology. 10 (2): 101–104. doi:10.1055/s-2007-994637. PMID8476469.
Bennett, S.; Cullen, J.; Sherer, D.; Woods Jr, J. (2008). "The Ferning and Nitrazine Tests of Amniotic Fluid Between 12 and 41 Weeks Gestation". American Journal of Perinatology. 10 (2): 101–104. doi:10.1055/s-2007-994637. PMID8476469.