Purpose: To evaluate the contribution of demographic and obstetric factors to birth stress as measured by salivary cortisol levels in healthy full-term infants. Materials and Methods: Ninety-three newborn infants were born vaginally after uncomplicated pregnancies in Japan. An observational study was conducted in 2009. Saliva was collected at one minute after checking Apgar scores and determined using a commercial high-sensitivity enzyme immunoassay kit. Results: In multiple linear regression analysis, length of second-stage labor [β (95% confidence interval) = 0.041 (0.022–0.059), standardized β = 0.452] and bleeding immediately after birth [β (95% confidence interval) = 0.006 (0.001–0.010), standardized β = 0.239] were mutually and independently associated with infant salivary cortisol levels. Conclusion: The length of second-stage labor and third-stage bleeding may be causative factors or factors reflecting the cause of infant stress. This finding also provides support for the use of salivary cortisol levels in evaluating infant stress.