As cell differentiation continues, the 'morula' becomes what is known as the 'blastocyst' by day 6 after fertilisation.
By the time the conceptus becomes a blastocyst (taking about 6 days) it enters the woman's uterus to implant in its thick lining (about a week before the woman's next period would have been due).

(post com data alterada - publicado a 04/08/2006)