The new findings suggest, but do not prove, that diabetes is a risk factor for depression in this group, researchers say.
Pregnant women and new moms in the study had nearly twice the incidence of depression as non-diabetic women who were pregnant or had just given birth.
The study included only low-income women, and it is not clear if the findings extend to other groups of pregnant women and new moms.
Study researcher Katy Backes Kozhimannil, who is a doctoral candidate at Harvard Medical School, tells WebMD that more research is needed to determine if diabetes plays a direct role in depression during and immediately after pregnancy.
"This is a potential new risk factor for postpartum depression, and we really don't have many of those," she says. "Diabetes and depression are both treatable illnesses. If we are able to show that women with diabetes are more vulnerable to postpartum depression we can target detection and intervention efforts to this group."
The study included just over 11,000 low-income New Jersey women receiving Medicaid who gave birth between July 2004 and September 2006.
Those with either pre-existing type 1 or type 2 diabetes or gestational diabetes were significantly more likely to experience depression during pregnancy or in the postpartum period.
After controlling for noneconomic risk factors for postpartum depression, women with diabetes had nearly double the odds of having a diagnosis of depression or taking antidepressantmedication in the months immediately following delivery, compared to women without diabetes.
About 10% of women with diabetes and no history of depression developed postpartum depression, compared to 6% of nondiabetic women with similar histories, Backes Kozhimannil says.
"These findings do not establish that diabetes is a cause of postpartum depression, only that they are related to each other in some way," she says. "There are certainly many unanswered questions, but this is the first study to examine this relationship and we need to pay attention to these findings."