In Fig. 2a, triangles represent the participants DLMO phase at 3rd Trimester (top) and 6 weeks postpartum (bottom). Most women phase delayed across the perinatal period. In Fig. 2b, circles represent the participants’ phase angles at 3rd trimester (top) and 6 weeks postpartum (bottom). Most women had a decrease in phase angle across the perinatal period, indicating they were going to sleep at an earlier circadian time, i.e., closer to the onset of nocturnal melatonin secretion.