OBJECTIVES: Little is known about risk of custody loss or out-of-home placement among children whose mothers experience postpartum mental disorders, and whether this risk differs from that of children whose mothers had earlier onset of their mental disorder.

METHODS: National Danish registers comprising 1 868 467 births (1982-2012) were used to determine how the timing of maternal illness onset influences out-of-home placement risk up to age 18 years among children exposed to a maternal mental disorder.

RESULTS: Compared to children unexposed to maternal mental illness, risk was higher for children exposed to a maternal mental disorder whose mothers had a first contact for a mental disorder in the 0-12 months of predelivery (8.17/1000 person-years; aIRR 4.56, 95% CI 4.08-5.09), the first 3 months postpartum (4.60/1000 person-years; 3.55, 2.95-4.26) and 4-12 months postpartum (6.49/1000 person-years; 3.93, 3.50-4.41). Risk was even higher for children exposed to a maternal mental disorder when illness onset was more than 1-year predelivery (9.11/1000 person-years; 5.48, 5.32-5.66).

CONCLUSION: Risk of out-home placement in children exposed to mothers with a new-onset postpartum mental disorder is almost as high as in children whose mothers have long-standing illness. A better understanding of the trajectories of these mothers and children is warranted.