This study aimed to investigate mother–infant interaction and infant development in women at-risk of postpartum psychosis (PP), with and without a postpartum relapse.

103 women (and their offspring) were included, 43 at-risk-of-PP because of a diagnosis of bipolar disorder, schizoaffective disorder or previous PP, and 60 with no current/previous mental illness or family history of PP. Of the at-risk women, 18 developed a psychiatric relapse within 4 weeks after delivery (AR-unwell), while 25 remained symptom-free (AR-well). Mother–infant interaction was assessed using the CARE-Index at 8 weeks' and 12 months' postpartum and infant development using the Bayley-III at 12 months' postpartum.

Women at-risk-of-PP as a group, regardless of whether they developed a psychiatric relapse within 4 weeks after delivery, had less synchronous mother–infant interactions and had infants with less optimal cognitive, language, motor and socio-emotional development than healthy controls. In particular, boys of at-risk women had the lowest scores in cognitive, language and motor development and in mother–infant interaction, while girls of the at-risk women had the lowest scores in socio-emotional development. The synchrony in the dyad predicted infant cognitive and language development. There was no evidence for a difference in mother–infant interaction nor in infant development between the AR-unwell and AR-well groups.

These results suggest that, while there is a lack of evidence that an early postpartum relapse in women at-risk-of-PP could represent a risk for the infant per se, maternal risk for PP may be associated with less optimal mother–infant interaction and infant development.

The perinatal period is a time of high risk of relapse for women with a history of bipolar affective disorder (BPAD). We describe the pregnancy management of women with BPAD and identify risk factors for postpartum relapse.

The case records of 78 women with BPAD referred to perinatal mental health services before conception, during pregnancy or the postpartum period, between 1998 and 2009 in Birmingham UK, were screened. In women who were managed during pregnancy, those who relapsed in the postpartum were compared with those who remained well.

Forty-seven percent of women with BPAD referred in pregnancy suffered postpartum relapse. Women who were unwell at referral, younger, with unplanned pregnancy, previous perinatal episodes or a family history of BPAD were more likely to suffer postpartum illness.

Identifying risk factors for postpartum relapse enables us to individualise the estimation of a woman's risk and modify care plans accordingly. Duration of wellness prior to pregnancy is not associated with a lower risk of postpartum illness and so it is imperative that all women with BPAD receive referral in pregnancy.