Plasma melatonin circadian rhythm disturbances during pregnancy and postpartum in depressed women and women with personal or family histories of depression.

OBJECTIVE: The purpose of this study was to test the hypothesis that disturbances in levels of plasma melatonin differentiate pregnant and postpartum women with major depression from matched pregnant and postpartum healthy comparison women.
METHOD: Participants were 25 pregnant women (10 with major depression, 15 healthy) and 24 postpartum women (13 with major depression, 11 healthy). Healthy comparison women were matched on the number of weeks pregnant or postpartum. Plasma melatonin levels for each subject were measured every 30 minutes, in dim light (<30 lux), from 6:00 p.m. to 11:00 a.m. The values of plasma melatonin levels were log-transformed, and calculations were determined for the following measures: baseline and synthesis onset and offset times, duration, peak concentration, and area under the curve. Groups were compared by analyses of covariance, with age, number of weeks pregnant or postpartum, breast-feeding status, and body mass index as covariates.
RESULTS: Morning melatonin levels from 2:00 a.m. to 11:00 a.m. were significantly lower in pregnant women with major depression relative to healthy pregnant women. However, these levels were significantly higher in postpartum women with major depression across time intervals relative to postpartum healthy women. Pregnant but not postpartum women with a personal or family history of depression, regardless of their current diagnosis, had significantly earlier melatonin synthesis and baseline offset times relative to women without a family history of depression. In pregnant healthy women but not pregnant women with major depression, melatonin levels increased during the course of pregnancy. This association was not found among postpartum women with major depression or postpartum healthy women.
CONCLUSIONS: Plasma nocturnal melatonin concentrations, particularly during morning hours, were lower in depressed pregnant women but elevated in depressed postpartum women relative to matched healthy comparison women. In addition, melatonin timing measures were advanced in pregnant women with a personal or family history of depression. These findings implicate disturbances in the regulation of the melatonin generating system in pregnancy and postpartum depression.