Sherk, Stephanie Dionne. "Prenatal Development". Gale Encyclopedia of Children's Health, 2006. Gale. Archived from the original on 1 December 2013. Retrieved 6 October 2013.
thefreedictionary.com
medical-dictionary.thefreedictionary.com
"germinal stage". Mosby's Medical Dictionary, 8th edition. Elsevier. Retrieved 6 October 2013.
web.archive.org
Sherk, Stephanie Dionne. "Prenatal Development". Gale Encyclopedia of Children's Health, 2006. Gale. Archived from the original on 1 December 2013. Retrieved 6 October 2013.