Aetiology
The aetiology is poorly understood and clinical consensus is lacking; the development of postnatal depression is likely to involve an interaction between psychological, social, and biological factors.[31]
For non-psychotic episodes of major depression, a specific relationship to childbirth has been challenged. It has been suggested that depression is no more common following childbirth, that the clinical presentation is no different from that for depression occurring at other times, and that the treatment options are the same (although pharmacological adjustments may be required for women who are breastfeeding).[32] Pregnancy and the postnatal period can be a time of enormous psychosocial upheaval for many new mothers, which may act as a potent environmental trigger for a depressive episode.
Hormonal fluctuations occurring between pregnancy and the postnatal period have been postulated as one potential causative factor for depression developing in the early postnatal period within a subgroup of patients.[33][34][35] Studies into the role of antenatal and postnatal stress hormones have yielded mixed results, and no major differences in the hormonal profile of women who develop postnatal depression have been reported to date.[31][36]
Possible causative factors include the following:
Psychiatric illness
A past history of a mood or anxiety disorder (whether perinatal or not) is the strongest risk factor for postnatal depression.[6][37][38][39][40][41]
All psychiatric diagnoses including anxiety, panic disorders, bipolar disorder, obsessive-compulsive disorder, posttraumatic stress disorder, and eating disorders, confer an increased risk for postnatal depression.[42] Postnatal depression is more likely to occur in women with a history of previous depression or anxiety.[37][38][39][40][41] Discontinuing psychopharmacological treatments increases the risk of postnatal depression in women with depression or a bipolar disorder.[43]
Women who experience antenatal depression have about a fivefold increased risk of developing postnatal depression, while women who experience antenatal anxiety have a threefold increased risk.[41]
Two longitudinal studies also found that hypomanic symptoms at day 3 predicted depressive symptoms at 6 weeks after childbirth.[44][45]
Psychosocial factors
Life events: there is a strong association between recent negative life events and postnatal depression.[46]
Poor social support: emotional and instrumental supports have been negatively correlated with postnatal depression.[37][38][47][48] Perceived social isolation was strongly predictive of depression in the postnatal period in a sample of black women with low incomes.[49] Marital problems during pregnancy and the lack of a supportive partner have been found to moderately increase the risk of postnatal depression.[38][50]
Psychological, sexual, and physical violence against women by their intimate partner during pregnancy are all independently associated with postnatal depression.[51][52][53][54][55]
Low income, financial strain, unemployment, and low social status have a small but significant predictive effect on postnatal depression.[38][49]
In the presence of clear psychosocial adversity and mild to moderate postnatal depression, the risk of subsequent depressive episodes may depend on the persistence of the adverse circumstances.[11]
The association between migration status and postnatal depression is unclear. Apart from the known general risk factors, a lack of proficiency in the host country language and having refugee or asylum-seeking status are also associated with an increased risk of perinatal mental disorders in migrant women.[56]
Personality traits
Familial and genetic factors
Vulnerability to postnatal depression within 8 weeks of delivery may be familial; among women with a history of major depression, 42% of those with a family history of postnatal depressive episodes experienced depression following their first delivery compared with 15% in women with no family history.[2] For women without a personal history of major depression, however, the importance of a positive family history is less clear.[59]
An Australian twin study[60] reported that genetic factors accounted for 26% to 49% of variance in postnatal depressive symptoms, while in a Swedish population-based cohort of 580,006 sisters, the heritability of perinatal depression was estimated between 44% and 54%, with 33% of the genetic variance unique for perinatal depression (i.e., not shared with depression at other times).[61]
One Danish registry study suggested that a family history of psychiatric disorders, especially bipolar disorder, in first-degree relatives is an important risk factor for broadly defined postnatal psychiatric disorders.[62]
Molecular genetic evidence is sparse.[63] Overall, there appear to be similarities in genetic polymorphisms associated with major depressive disorder in the non-perinatal population.[63][64] There is also some evidence that postnatal depression may have unique genetic components, which are distinct from those that increase susceptibility for major depressive disorder in the non-perinatal population.[65]
One genome-wide linkage study suggested that genetic variation on chromosomes 1q and 9p might increase susceptibility to broadly defined postnatal mood symptoms in one sample of women with both unipolar and bipolar disorder.[66]
Sleep deprivation
Sleep changes in pregnancy are associated with depressive symptoms in the postnatal period, suggesting sleep timing may be a modifiable risk factor for developing postnatal depression.[67][68] A strong association between infant sleep patterns, maternal fatigue, and new-onset depressive symptoms in the postnatal period has been suggested. Therapeutic interventions to reduce sleep deprivation in the early postnatal weeks have been tried,[69] but results are inconclusive.[70]
Complications of pregnancy and birth
Young maternal age
One study found that mothers under 16 years of age are at higher risk of postnatal depression.[39]
Pathophysiology
The exact pathophysiology is not known, but there is some evidence to suggest that hormone factors, genetics and immune function may play a role.[35][72][73] Postnatal depression may encompass a number of distinct depressive phenotypes, given that there exists substantial variation in risk factors and clinical presentations between patients, such as timing of onset and past history of depression.[74] It has been suggested that a subgroup of women who become depressed after childbirth may have an abnormal sensitivity to the normal physiological changes of childbirth.[33] It has also been suggested that the inflammatory response after labour and delivery may be exaggerated in women who develop postnatal depression.[75]
Classification
Commonly used
Postnatal affective disorders are typically divided into three categories.
Minor mood disturbance
Postnatal blues, or 'baby blues', is a common but transient condition affecting 30% to 80% of women following childbirth.[8] Women can also experience symptoms of hypomanic mood (the 'highs') at this time.[9][10]
The mother typically presents with mood swings ranging from elation to sadness, insomnia, tearfulness, crying spells, irritability, anxiety, and decreased concentration. Symptoms develop within 2 to 3 days after delivery, peak on the fifth day, and resolve within 2 weeks.
Minor mood disturbances do not need treatment, but may indicate an increased risk of developing a clinically significant mood disorder later in the postnatal period.[11]
Postnatal depression
Episodes of clinical depression occur commonly following delivery and may cause significant disruption to the woman and her family. Around 10% of mothers experience clinically significant depressive symptoms during the first 6 months following childbirth, although not all receive treatment.
In contrast to minor mood disturbance, episodes of postnatal depression can last for months or even years and can result in significant impairment with severe long-term consequences.
Postnatal psychosis
The most severe forms of postnatal mood disorder have traditionally been labelled as postnatal (or puerperal) psychosis. Although the disorder is not easy to define, the core feature is the acute onset of a manic, mixed, or depressive psychosis in the immediate postnatal period.
Postnatal psychosis occurs following 1 in 1000 deliveries and is a psychiatric emergency.[12][13] Postnatal psychosis may rarely occur in unipolar depression, but is more typically associated with bipolar disorder.[13]
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