[Dynsei]

"Paeonia has been shown to positively influence low progesterone, reduce elevated androgens (testosterone) and acts to modulate estrogen and prolactin." ...

http://www.townsendletter.com/Nov2004/phyto1104.htm

I think that means it also lowers progesterone. It could be because it raises estrogen. through aromatase. Estrogens and progestogens lower each other. The rest of the quote was interesting about the active ingredient, about feedback and the dosage.

Corpus luteum is some form of the egg, I forget which. It is a temporary organ that produces progestogens, until menstruation.