At approximately day 1

Leydig cells decrease by apoptosis, to very low amounts at birth. Leydig cells then proliferate again 2-3 months after birth, and again at puberty.

Duration: 1 week

Reference [PubMed Link]

Prince FP. 2001. The triphasic nature of Leydig cell development in humans, and comments on nomenclature. J Endocrinol 168(2):213-6.