Earlier studies looked into possible links between bipolar disorder or schizophrenia and prenatal exposure to the influenza virus. However, a big problem with much of the previous research is that it was based on mothers’ memories of their health during pregnancy—memories that typically are decades old (and thus prone to inaccuracy), given that those psychiatric illnesses usually appear in early adulthood.
The recent study used a different investigational approach to get around that problem. Researchers had access to medical information from a very large group of women who were cared for during their pregnancies by a major health-care organization (Kaiser Permanente) in a California county from 1959 through 1966. By using actual medical records—not just relying on moms’ memories—the researchers determined which women had become sick with the flu while pregnant. (Because flu vaccination was not common in the late 1950s and early 1960s, only 6% of the mothers in the study received flu shots at the time.)
Disturbing findings: People born to mothers who had the flu at any time during pregnancy were nearly four times more likely to develop bipolar disorder, compared with people whose mothers did not have the flu while pregnant. The risk was even more pronounced when the mothers contracted the flu during the second or third trimester of pregnancy rather than early in pregnancy. The link between prenatal flu exposure and subsequent bipolar disorder remained even after researchers adjusted for other possible risk factors, including the mothers’ own history of psychiatric disorders.
Schizophrenia connection: Interestingly, these same researchers using the same databases had previously found that influenza exposure in early to mid-pregnancy was associated with a threefold increased risk for schizophrenia, though flu exposure in late pregnancy was not linked to increased schizophrenia risk. The researchers theorize that exposure to the flu might give rise to different mental disorders among offspring depending on when during pregnancy an expectant mother gets sick.
Preventing future problems: There’s no need to panic, the researchers noted, because the vast majority of babies born to mothers exposed to the flu will not get bipolar disorder or schizophrenia. Still, it’s better to be safe than sorry. So to help safeguard the future mental health of their children, the researchers suggested that women who are pregnant or trying to become pregnant should take care to avoid contact with people who have flu symptoms…and should get seasonal flu vaccinations as early in the season as possible.