The exact cause of postpartum depression is not clear. The underlying reasons for postnatal depression are complex and, often, a combination of risk factors are at play. Some of the factors that may cause or raise the risk of postpartum depression include:

• Depression during pregnancy.
• Previous history of mood disorders such as bipolar disorder or depression.
• A difficult labour or complicated childbirth.
• Pain after labour or other complications such as urinary incontinence.
• Hormonal changes: Sharp changes in hormonal levels after childbirth are thought to contribute to postpartum depression. Hormonal changes may lead to some degree of low mood and irritability in all mothers but in cases of postpartum depression, these mood changes do not subside.
• Social issues such as relationship problems, lack of social support (e.g. among single or teenage mothers) and a lack of close family and friends are factors that may raise the risk of depression after childbirth.
• Financial worries are another trigger factor for postpartum depression.
• Unrealistic or high expectations a mother has about her ability to acquire mothering skills quickly after childbirth can lead to depression if she does not realise these.
• Exhaustion and stress due to lack of sleep or because the baby has colic or other health problems.
• Family history of clinical depression, especially among first degree relatives such as siblings or parents.
• Women who have a substance abuse problem or have stopped using certain medications during pregnancy and after childbirth may be at risk.