delayed implantation

[Whitney Price]

Does anyone know the mechanism that causes the delayed implantation
following fertilization after gerbil birth?  I'm a bit curious after my
class this week on human fertilization, morulae, blastocysts, nidation and
all that other *fun* stuff (well, it sure beats my *other* lecture this
week--on respiratory anatomy/physiology/patho...WHOO-boy!)