diurnal patterns
After, not before, you get to the hospital, I always say.
But seriously, Robert Martin, the famous primatologist, has an interesting piece in Psychology Today exploring this question. Go read it. I've got a few thoughts spurred by this research I'll list briefly here.
First, it seems that wild primates give birth during their daily down-time, the period of time that they are generally inactive. Dirunal primates do so more at night, nocturnal primates do so more during the day. Various reasons have been proposed. I've not read the primary literature on this, but in my ignorance I wanted to…