Participants were 120 primaparous women who had vaginal delivery of a non-handicapped child. Saliva was collected twice daily through parturition to day 35 post-partum. In the prepartum, a highly significant circadian rhythm was seen in cortisol, with a lower-amplitude rhythm in progesterone (AM/PM = 1.12). Evening samples showed a rise in cortisol, with a highly significant rise on day -1. The rise was small. The fall in progesterone in the 3 days before parturition was also small (approximately 6%). Neither change provides an obvious trigger for parturition.