Postnatal psychosis more common in older first-time mothers

Women who give birth for the first time after the age of 35 run a greater risk than younger first-time mothers of suffering a psychosis in the months after delivery.

This according to a study from Karolinska Institutet published in the latest issue of the open access scientific periodical PLoS Medicine.

Unlike postnatal depression, a psychosis directly after childbirth (postpartal psychosis) is relatively rare, but can have serious, lasting consequences for both mother and child, as well as the people around them. The reason why this affects only some women is not fully understood.

In the present study, scientists from the Department of Medical Epidemiology and Biostatistics (MEB) used data from the Swedish Medical Birth Register on almost 750,000 first-time mothers in Sweden who gave birth between 1983 and 2000. In their examination of the risk of developing a psychotic illness during and after the 90 days following childbirth, the researchers looked particularly closely at the group of first-time mothers who lacked a documented history of psychiatric hospitalisation. Comparisons were made on the basis of several background factors, such as age, education and delivery characteristics.

"We know from previous studies that women who've had a previous psychiatric condition are more likely to develop postpartum psychosis," says Unnur Valdimarsdóttir, one of the researchers involved in the study. "Our intention in this study was to identify factors that increase the risk of postpartum psychosis in women without a history of psychiatric hospitalisation."

What they found was that 892 of the women (1.2 in every 1,000 births) received hospital treatment for a psychotic illness within 90 days of their first delivery. Of these, 436, or almost 50 per cent (0.6 of every 1,000 births) became ill for the first time. After the 90 days had passed, the risk of developing a psychosis decreased for all mothers.

The team could also see a direct correlation between age and risk of postpartum psychosis, in that those who were 35 or older when they had their first child were 2.4 times more likely to suffer a psychosis than first-time mothers of 19 or younger. On the other hand, high birth weight and maternal diabetes also correlated with a lower risk of psychosis.

"Anyway, the most important finding is that the risk of psychosis increases sharply in close relation with the birth of a first child for women both with and without a previous psychiatric diagnosis," says Dr Valdimarsdóttir. "More studies are needed before we understand any explanatory mechanisms, such as hormonal changes during labour."