There's a growing body of evidence about the dangers of contracting the flu during pregnancy. The most recent is a study published today in JAMA Psychiatry that found a strong association between flu infection in a pregnant woman and bipolar disorder (BD) in her child later in life.

The study was conducted by scientists at Columbia University, Kaiser Permanente, and the Albert Luthuli Central Hospital in Durban, South Africa, and was funded by grants from the National Institute of Mental Health and the National Institute on Child Health and Development.

Researchers examined a birth cohort from the Child Health and Development Study (CHDS) and county healthcare databases in Northern California. They confirmed 92 cases of bipolar disorder among 214 study participants and 722 control subjects.

“Offspring exposed to maternal influenza infection at any time during pregnancy were nearly four times more likely to develop BD than those who were not exposed,” the researchers concluded.

Alan S. Brown, M.D., a professor of clinical psychiatry and clinical epidemiology at Columbia University, was one of the study's authors.

When asked how viruses, such as those that cause the flu, can affect an unborn child, Brown said, "We don't know for sure, but activation of the immune system is a good candidate.”

If confirmed by other birth cohort studies, these new findings may have implications for the prevention of BD, the study authors say.

Dangers of Getting the Flu While Pregnant

Only a small proportion of the pregnant women in the sample population (6.1%) received a flu vaccination, though studies have shown that receiving the flu vaccine while pregnant does not raise the risk of miscarriage or fetal death.

A number of previous studies, some inconclusive, have linked maternal influenza to psychological illnesses in children, including schizophrenia, BD, and psychosis. In particular, the studies on schizophrenia and BD are beginning to shed light on the similarities and differences in the pathogenic mechanisms that cause these conditions.

“There may be unique and shared causes between these two disorders," Brown said. "Our finding suggests one shared cause because we previously found that maternal influenza was associated with schizophrenia in offspring.”

What Is Bipolar Disorder?

Bipolar disorder is a manic-depressive illness that causes severe mood swings that can affect every aspect of life, from relationships to academic performance. The risk for suicide is very high among people with BD—10 to 15 percent by some estimates.

Bipolar spectrum disorders affect about 5.7 million people, or about 2.6 percent of U.S. adults, each year, according to the National Institute of Mental Health. The average age of onset is 25 years. In early-onset bipolar disorder, the risk of suicide increases to 30 percent or higher. 

An Ounce of Prevention

The primary exposure the researchers studied was influenza. However, they also analyzed data on a group of other respiratory tract infections, including tuberculosis, diphtheria, pertussis, cold, sinusitis, tonsillitis, pneumonia, bronchitis, rhinitis, and laryngitis.

Given the growing body of evidence linking maternal flu to health problems in one's offspring, pregnant women should take care to avoid people with symptoms of respiratory infections and to get a flu shot before or during pregnancy to ensure the safety of their unborn children.

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