Table 1. Representative steroid concentrations in the woman at different reproductive phases.

Reproductive phase	Steroid	Tissue	Concentration (ng/mL)	Source
Follicular	Progesterone	Plasma	1.5	[43]
		Brain	–	–
	Allopregnanolone	Plasma	0.15	[43]
		Brain	2.4	Estimated*
Luteal	Progesterone	Plasma	10	[43]
		Brain	41	[43]
	Allopregnanolone	Plasma	1.2	[43]
		Brain	20	[43]
Late pregnancy	Progesterone	Plasma	204	[44]
		Brain	–	–
	Allopregnanolone	Plasma	16	[44]
		Brain	260	Estimated*

* = estimated from the brain/plasma ratio at the luteal phase.