Swine Flu and Pregnancy

October 16, 2009

Why expectant mothers should get the swine flu vaccine — a new study shows that the H1N1 pandemic in 1918 affected the subsequent health of babies in utero.

People exposed to an H1N1 strain of influenza A while in the womb were significantly more likely to have cardiovascular disease later in life, according to research published in the Journal of Developmental Origins of Health and Disease.

“Our point is that during pregnancy, even mild sickness from flu could affect development with longer consequences,” says senior author and University Professor Caleb Finch of the USC Davis School of Gerontology.

Finch, USC Davis School professor Eileen Crimmins, lead author Bhashkar Mazumder of the Federal Reserve Bank of Chicago, Douglas Almond of Columbia University, and Kyung Park of the University of Chicago looked at more than 100,000 individuals born in and around the time of the 1918 influenza pandemic in the United States.

After first appearing in the spring and all but disappearing in the summer, the 1918 pandemic “resurged to an unprecedentedly virulent October-December peak,” the researchers write. The outbreak of H1N1 subtype influenza A killed 0.6 percent of the total population. Most people experienced mild “three-day fever” with full recovery.

“The 1918 flu was far more lethal than any since. Nonetheless, there is particular concern for the current swine flu, which seems to target pregnant women,” Finch says. “Prospective moms should reduce risk of influenza by vaccination.”

The researchers found that males born in the first few months of 1919 — who were in the second or third trimester during the height of the epidemic — had a 23.1 percent greater chance of having heart disease after the age of 60 than did the overall population.

Among women, those born in the first few months of 1919 were not significantly more likely to have cardiovascular disease than their peers; this points to possible gender differences in the effects of flu exposure. But females born in the second quarter of 1919 — who were in the first trimester during the height of the epidemic — were 17 percent more likely to have heart disease in later life.

The researchers also examined heights from World War II enrollment for 2.7 million men born between 1915 and 1922. They found that average height increased every successive year, except for the period coinciding with fetal exposure to the flu pandemic.

According to the study, men who were exposed to the H1N1 flu in the womb were slightly shorter on average than those born just a year later or earlier.

“Prenatal exposure to even uncomplicated maternal influenza can have lasting consequences later in life,” Crimmins concludes.