Post-Partum Psychosis: Which Women Are at Highest Risk?

In a new study published in PLoS Medicine, Unnur Valdimarsdóttir and colleagues have investigated the clinical incidence of psychotic illness and its risk factors up to 90 days post-partum in a large case register study of firsttime Swedish mothers [2]. This study investigates an important problem, since the effects of maternal psychosis on attachment and infant care in the post-natal period can have lifelong adverse sequelae for mother and child [1]. The researchers argue correctly that whilst previous psychiatric illness is a well known risk factor for postpartum psychosis, it is not known how much other independent risk factors, such as obstetric complications, may be relevant. Only by studying first-time mothers with first psychotic episodes in the post-partum period can these independent risk factors begin to be elucidated. Valdimarsdóttir and colleagues used a large (n = 745,596) national case register of hospital discharges over a 17-year period in Sweden. The study accorded with the STROBE guidelines for reporting cohort studies [3], and has a number of strengths. These include the large and representative sample, clear hypotheses, and appropriate statistics (estimating risk with proportional hazard regression models). There are two noted limitations. First is the lack of data on women with post-partum psychosis who are not hospitalised, although this would be rare. Second, this is an observational study—and while such studies are very good for raising further questions, they are less robust in drawing definitive explanations. During the first 90 days post-partum, 892 women (1.2 per 1,000 births) were recorded as having been hospitalised due to psychoses. As expected, incidence rates for psychosis peaked in the first month after birth (285 of the 892 hospitalisations were in the first seven days, and 523 were in the first 14 days). About half of the hospitalisations (n = 436) were of women who had no previous psychiatric hospitalisation [2]. Specific to the first 90 days post-partum (but not later), higher maternal age was associated with increased risk of psychosis, and higher infant birth weight and maternal diabetes appeared protective. There was a different pattern of risk factors in the second 90-day period and in all women (i.e., including those with previous psychiatric hospitalisation). Overall, these findings suggest that there is a specific independent risk for psychosis in the early post-partum period.