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Postnatal depression is a lot more complex - and debilitating - than having a case of the "baby blues". Over half of mums will experience the baby blues.
But around one in five women will experience a mental health problem during pregnancy or in the year after giving birth, such as postnatal depression.
Symptoms which identify postnatal depression include; a persistent feeling of sadness and low mood, loss of interest in life, feelings of guilt and self-blame and low self-confidence.
However, there's one sign which typically gets overlooked - but which could be a key indicator of a new mum or dad's state of mind.
And failure to identify it could be delaying the recovery of a parent with postnatal depression.
Most women are screened for anxiety and depression, according to a study by the University of British Columbia , but they're not being screened for anger.
What's more, the Edinburgh Postnatal Depression Scale screening tool (commonly used to help reach a diagnosis) doesn't even feature anger. Nursing PhD student Christine Ou conducted the study, and discovered the large role anger in fact plays in postnatal depression. So much so, it can even hinder a woman’s recovery if left untreated.
"We know that mothers can be depressed and anxious in the postpartum period, but researchers haven’t really paid attention to anger," Ou told the University of British Columbia. "There’s some evidence that indicates that being both angry and depressed worsens the intensity and length of depression.
"That can have many negative effects on the mother, child and family, and on the relationship between parents."
Ou believes this anger in part stems from feeling their parenting is being judged, as well as not having the support they need from their loved ones.
"Mothers may feel that they have not met their own expectations and that also others may judge them because, for example, they’re formula-feeding instead of breastfeeding," she told the University of British Columbia.
"Many mothers have also expressed feeling let down by others in terms of support from partners, family members, and health-care providers as well."