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Postpartum depression (PPD) is one of the most common complications of childbirth around the world. Despite several studies on the underlying mechanisms, the pathophysiology remains elusive. The aims of this thesis were to assess possible associations between the risk for self reported PPD and serum levels of leptin, the season of delivery, the gender of the newborn, and the history of premenstrual symptoms, respectively.

A population based cohort of 2318 newly delivered women in Sweden were screened five days, six weeks and six months postpartum, using the Edinburgh Postnatal Depression Scale. This cohort comprised 60% of the total population, and the prevalence of self reported PPD was 11.1% six weeks after the delivery.

A negative association between leptin levels at delivery and self reported PPD at six weeks and six months postpartum was evident, even after adjusting for confounding factors. 

An increased risk for self reported PPD was noted among women delivering during the last three months of the year, compared to those giving birth in April through June. This is of clinical importance, since women delivering at the end of the year could benefit from a closer follow-up after delivery. 

Despite previous varying findings – depending on study population and consequently different cultural settings – in our study, no association between infant gender and self reported PPD could be detected at six weeks or six months postpartum. However, women giving birth to baby boys had a higher risk for postpartum blues.  

Lastly, an increased risk for self reported PPD among women with a history of premenstrual symptoms was noted. Interestingly, after stratification for parity, the association between PPD and premenstrual symptoms remained only among multiparas. The association between PPD and premenstrual symptoms might shed light on the many possible routes by which hormonal changes may influence mood in women.

In conclusion, this population based study strengthens the notion that PPD is a complex multifactorial disorder, with biological, social and psychological parameters shaping each individual’s risk.  Further research is needed in this field, in order to investigate underlying pathophysiological mechanisms, propose more effective diagnostic tests and assess therapeutic interventions.