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.