First-time mothers at a greater risk of psychosis in the month following childbirth

A study of risk factors associated with psychotic illness after childbirth, published this week in the open-access journal PLoS Medicine, shows that first-time mothers are at the greatest risk of developing psychosis in the month following the birth of their child - even if they have never been treated in hospital for mental illness in the past.

It can be common for mothers to experience mental illness in the post-partum period (the months following childbirth): most frequently these might involve short-lived cases of the "baby blues" in the days after birth, and mild to moderate postnatal depression in the weeks and months that follow. Psychotic illness (a mental condition involving episodes where the individual is unable to distinguish between reality and their imagination) in the post-partum period is relatively rare. Only around one in every 1,000 women develops psychosis after delivery, but it is dangerous for mother and child, with greater risk of self-harm and suicide. The causes of post-partum psychosis are not well understood. Unnur Valdimarsdottir, of the Karolinska Institutet in Stockholm, and colleagues investigated the rates of psychosis in first-time mothers up to 90 days after the birth of their child, and a number of possible risk factors for psychosis, in Sweden between 1983 and 2000.

Sweden has excellent conditions for this research because it has population-based registers covering almost all births and inpatient records. The researchers therefore had a representative sample - they were able to identify nearly three quarters of a million first-time mothers in Sweden in this period and found that 892 had been admitted to hospital for psychosis within 90 days of giving birth (a rate of 1.2 cases for every thousand births). About half of these women had no previous record of being hospitalized for any psychiatric illness. Amongst the women who developed psychosis, the incidence rate was highest during the first month following birth and it dropped to a tenth of that initial rate at 90 days after birth. Furthermore, the research established that the risk of developing psychosis increased with maternal age: women older than 35 were at two times greater risk than women aged 19 or less. Factors associated with less risk of psychosis in the population of women studied were higher infant birth weight and maternal diabetes; other factors, including smoking and not living with the infant's father, had no or limited impact on the risk of psychosis during the postpartum period.

The study therefore suggests that there is a specific risk of first-time mothers developing psychosis in the early period after childbirth. This finding highlights the importance of carefully monitoring women in the first month after delivery. However, the authors recognise that their findings cannot determine exactly why the risk of psychosis is greatest a month after delivery. They suggest several explanations, including the idea that women are at greater biological vulnerability in this period due to the profound hormonal fluctuations they experience.

In an expert commentary on the new study, Phillipa Hay (University of Western Sydney), uninvolved with the research, says: "it is unlikely that there will be any single explanation, and that biological factors will be independent of others." Hay argues that other interdependent risk factors, including biological, social and psychological factors, may contribute to post-partum psychosis in first-time mothers, and that by elucidating these risk factors we may "reduce the impact and burden" of this devastating illness.