during pregnancy three peaks of progesterone stood out : ( 1 ) when implantation starts , ( 2 ) when older sets of corpora lutea showed rejuvenation and placental signs were found in the vaginal smears , and ( 3 ) 3 days before expected parturition when luteal development ( as judged by histology ) reached a peak .
C0032961
pregnancy
C0033308
progesterone