When a pregnant woman is told to avoid alcohol, cigarettes, certain medications and even hot tubs—all of which can hurt an unborn baby’s development—it’s pretty easy for her to stay away from these risks.

But there’s another hazard lurking out there that also can harm a baby’s development in a big way, a new study cautions…because if an expectant mother is exposed, it could quadruple her child’s risk for bipolar disorder, a very serious mental illness.

What is this threat? It’s the flu…


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.)

During that seven-year timeframe, more than 19,000 babies were born to these women. Researchers followed those children for up to 29 years by looking at the databases of both the HMO and the county’s behavioral health-care services and by sending mailings to all the mothers and children. Among the people born to the mothers in the study, the researchers identified 92 who had gone on to develop bipolar disorder. For comparison’s sake, these patients were matched with 722 otherwise similar people who did not have bipolar disorder.

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.

According to the latest data from the Centers for Disease Control and Prevention, half of pregnant women fail to get the flu vaccination before or during their pregnancies. In some cases, this may be due to concerns about the safety of vaccination during pregnancy. However, several recent large studies found that pregnant women who got flu vaccinations were no more likely to miscarry, experience pregnancy complications or have children with birth defects than pregnant women who did not receive flu vaccinations.

The nasal spray flu vaccine, which contains a live attenuated (weakened) form of the influenza virus, is not appropriate during pregnancy. Instead, expectant mothers should receive the inactivated flu vaccine, which comes in the form of a shot. Remember, for maximum protection, flu shots must be repeated each year because the virus changes from season to season.

Flu info for everyone (not just pregnant women): For up-to-date information on this year’s flu vaccine options, read The New Four-Strain Flu Vaccine: Is It Right for You? To learn how to strengthen your immune system and help your body fend off flu and other infections, read Boost Your Immunity to Fight Colds, Flu and Pneumonia.