Pregnant women with bipolar disorder have a significantly higher risk of developing postpartum psychosis than other mothers, researchers say.

Researchers at Northwestern Medicine, Stanford University and Erasmus Medical Center in Netherlands reviewed literature on the underresearched disorder, which increases the risk of a mother harming herself or her child. It affects two mothers in 1,000 and differs from postpartum depression, which is experienced by one in seven women, often involving delusions or hallucinations. Other symptoms include frequent crying, anger, anxiety, withdrawal from loved ones, the feeling of numbness or being disconnected from the baby and sometimes thoughts of hurting oneself or the infant, the American Psychological Association says.

There are few experts on postpartum psychosis because there are so few cases.

The problem is compounded by a reluctance by to prescribe lithium, which is the most effective and fast-acting drug to treat postpartum psychosis, to breastfeeding mothers, fearing it would have an adverse impact on the baby, said lead author Dr. Katherine Wisner, the Norman and Helen Asher Professor of Psychiatry and Behavioral Sciences and Obstetrics and Gynecology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine psychiatrist. The review was published by the American Journal of Psychiatry.

"More often than not, the risk of the medication is less than the risk of the uncontrolled disorder," Wisner said in a press release. "This is a really serious disorder, and no one likes to treat women with medication during pregnancy or breastfeeding, but there's certainly very high risk in not treating as well, such as the risk for suicide," Wisner said.

Perhaps the best known case of postpartum psychosis involved Andrea Yates who drowned her five young children, ages 6 months to 7 years, in a bathtub in her suburban Houston home. She then called 911.

Her attorneys said she suffered from psychotic delusions, had multiple violent visions of murder and tried to commit suicide before killing her children, Time reported.

Fifteen years after the killings, she lives at the Kerrville State Hospital, a Texas mental health facility. People reports she watches videos of her children laughing and playing.

Her conviction in the July 20, 2001, deaths was overturned in 2006, when she was found not guilty by reason of insanity.

Wisner said nearly everyone knows a woman with bipolar disorder since the condition affects as much as 5 percent of the population.

“These women need to be aware that postpartum psychosis is a possibility and that there are preventive treatments that are highly effective,” Wisner said.