Postnatal depression is the most common complication of childbirth affecting up to 14.5% of new mothers in the first three months after childbirth. There has been little research into whether postnatal depression varies across the seasons so a team of researchers from the University of Pittsburgh studied this issue in 9,339 new mothers. They screened the mothers for depression four to six weeks after the birth of their child and looked for seasonal variations in levels of depression and suicidal ideation (thoughts of killing oneself). They found that 14% of the women had significant levels of depression and 3% of them had had suicidal thoughts. Although the risk for depression varied over the year with the highest risk being in December there was no seasonal variation in suicidal thoughts.
Sit, Dorothy, Seltman, Howard and Wisner, Katherine L. - Seasonal effects on depression risk and suicidal symptoms in postpartum women Depression and Anxiety DOI 10.1002/da.20807