luteoplacental shift
Definition: the change in site of production of the estrogen and progesterone essential for human pregnancy from the corpus luteum to the placenta; ovariectomy always terminates pregnancy in most mammals because their placentas never produce enough estrogen and progesterone, but, after the sixth week of pregnancy, a human placenta can produce enough of these hormones to prevent abortion despite ovariectomy.
Search Stedman's Medical Dictionary
Examples: glitazone, GI cocktail, etc.

