The absolute risk for women with an affected sibling was estimated to be 1.6% for the entire population.
Women whose sisters had postpartum psychosis were more than 10 times more likely to develop it than other women, according to research presented at the American Psychiatric Association Annual Meeting.
Risks for postpartum psychosis also were elevated among women whose cousins had it as well, Veerle Bergink, MD, PhD, professor in the department of psychiatry at the Icahn School of Medicine at Mount Sinai, told attendees.
Postpartum psychosis is one of the most severe psychiatric conditions, with high risks for suicide and infanticide if untreated, Bergink said., But although genetic factors contribute to the risk of postpartum psychosis, she continued, the extent of familial risk remains to be determined.
"What we do know is who is at risk," Bergink said.
"Women with bipolar disorder, manic depressive illness, are at very high risk of getting sick after delivery.".
Without medication, she said, the relapse risk was more than 50%.
As prior research has found that postpartum psychosis occurred more in women with bipolar disorder as well as a family history of the condition, Bergink and colleagues sought to compare relative recurrence risk across different family relationship types.
Also published in the American Journal of Psychiatry, their retrospective cohort study culled data from the Medical Birth Register in Sweden between January 1980 and October 2017.
A total of 1,648,759 women, of whom 2,514 (0.15%) experienced postpartum psychosis within 3 months of their first-ever childbirth, were included. This cohort included 876,084 full siblings and 461,026 cousins.
Siblings and cousin pair information within this dataset was taken from the Multi-Generation Register, which has collected parental records on individuals born in Sweden since 1932. Diagnostic information was acquired from the Swedish National Patient Register, which included both inpatient and outpatient records from each respective subregister.
The researchers included three covariates for analysis: year of the first birth, age of the mother at first birth and familial history of bipolar diagnosis. They then utilized conditional logistic regression to estimate relative recurrence risk of postpartum psychosis for full sisters and cousins as a measure of familial risk for those with a history compared to those without.
Results showed that, from the cohort of those with postpartum psychosis within 3 months of their first birth, 1,234 individuals (49%) had a prior history of bipolar disorder and another 605 (24%) had other mental health diagnoses.
Beergink further revealed that a mother is more than 10 times more likely to have postpartum psychosis if her sister had the condition (relative recurrence risk = 10.69; 95% CI; 6.6-16.26) when adjusted for year of and age at childbirth.
"This is higher than really severe diseases in psychiatry, such as bipolar disorder, which has been shown in the Swedish register at 7.9, and schizophrenia in other studies, 9.0," Bergink said.
Although cousins showed an elevated relative recurrence risk, it did not attain statistical significance (1.78; 95% CI= 0.7-3.62).
The researchers additionally reported that the prevalence of bipolar disorder in the whole dataset was 1.4% (n = 22,993) and although a higher familial risk existed for full siblings, the absolute risk for women with an affected sibling was estimated at 1.6% within the entire population.
"I think that is a really assuring message for family members," Bergink said, adding that this risk is still low.
Data also showed the estimated prevalence for postpartum psychosis was 0.15%, consistent with previous reports in Sweden between 1975 and 2003 as well as from 1983 to 2000.
"What to do (for individuals whose partners may be at risk) is what normally would be wise to do after delivery anyway," Bergink said. "To make sure someone sleeps well, to make a deal with your partner if possible, taking over the night feedings and don't go crazy about breastfeeding if it doesn't work."
But Bergink also said that physicians have 9 months to prepare for possible postpartum illness and potentially prevent episodes.
"We know that for women who are medication free to start prophylaxis right after delivery," she said. "We're really advocating for starting lithium or, if they don't want that, a psychologist right after delivery."