Table 2.

Endometrial shedding in the neonate and reproductive outcome

ENDOMETRIUM DEVELOPMENT
At birth
NORMAL PREGNANCY	FETAL DISTRESS
Progesterone resistant	Progesterone responsive
No bleeding	Neonatal menstruation
At menarche
Persistence of progesterone resistance	Menstrual preconditioning
Defective deep placentation
Risk of endometriosis
Risk of preeclampsia	Normal pregnancy

During pregnancy, the fetal endometrium remains progesterone-resistant except when fetal distress causes decidualisation and menstruation at birth.

During infancy, the endometrium remains progesterone-resistant, but the onset of ovarian activity causes shedding and preconditions the endometrium for progesterone response and normal menstruation.

In the absence of adequate preconditioning, very young girls are exposed to defective deep placentation and the risk of preeclampsia.