The risk of bipolar affective puerperal psychosis - a severe mental illness following childbirth - is highest after the birth of a first baby, a new study has confirmed.

Research has shown that women with bipolar disorder are at greatly increased risk of an episode of the illness immediately after childbirth.

Previous studies have also highlighted a number of factors that may be associated with the development of puerperal psychosis. These include the birth of a first baby, pregnancy complications, delivery complications, Caesarean section, and having a female baby and a shorter pregnancy.

In this study, published in the January 2006 issue of the British Journal of Psychiatry, the researchers examined a sample of 129 women with bipolar affective puerperal psychosis. All were interviewed by a trained psychiatrist or psychologist and information was obtained from case notes.

The authors of the study were able to examine a number of the risk factors implicated by previous studies, both separately and in combination, and, uniquely, were able to make comparisons with the unaffected deliveries of women with puerperal psychosis.

They confirmed that having a first baby was associated with a higher risk of puerperal psychosis. It is likely, they say, that hormonal, immunological and other biological differences between first and later pregnancies may explain these findings, and may suggest candidate genes for molecular genetic studies of puerperal psychosis.

The study also found that although complications in pregnancy were not associated with an increased risk of the illness, experiencing a complication during delivery more than doubled the risk.

It may be that complications during delivery cause a magnified stress response, producing particularly high or prolonged levels of the hormone cortisol. Or complications may be associated with prolonged labour that results in excessive sleep disturbance.

As with first birth, there is also the potential for obstetric complications to lead to (or reflect) altered immunological interaction between the mother and the foetus.

No significant relationship was found between puerperal psychosis and the other risk factors - Caesarean section, having a female baby or preterm delivery.

The authors of the study conclude that psychological and biological differences between first and subsequent deliveries, and between women with and without obstetric complications, are important avenues for further research.

Increasing understanding of the risk factors associated with puerperal psychosis has implications for the identification and treatment of women at risk, and may also give important clues to the causes of affective disorders both at birth and at other times.

http://www.rcpsych.ac.uk