People who were exposed to the 1918 pandemic flu virus in utero were more likely to have cardiovascular problems later in life, a new U.S. study suggests.

The findings raise questions about the long-term effects of exposure to pandemic flu viruses in the womb.

'During pregnancy, even mild sickness from flu could affect development with longer consequences.'— Caleb Finch

"Our point is that during pregnancy, even mild sickness from flu could affect development with longer consequences," said study author Caleb Finch, a professor of gerontology and biological sciences at the University of Southern California.

Researchers analyzed data from more than 100,000 Americans who were born during and around the time of the 1918-1919 influenza pandemic.

Men who were born in the first few months of 1919, when their mothers were in their second or third trimester during the peak of the pandemic, had a 23.1 per cent greater chance of heart disease after age 60 than the overall population, the team reported in Thursday's issue of the Journal of Developmental Origins of Health and Disease.

Women were 17 per cent more likely to have heart disease than the general population in later life, if they were born in the second quarter of 1918.

Height difference

Finch's team also looked at the height of 2.7 million men born between 1915 and 1922 when they enrolled in World War II.

Men who were exposed to pandemic flu in the womb were slightly shorter on average than those born just a year later or a year before, the researchers found, after taking into account the effect of seasons at birth and maternal malnutrition.

The pandemic strain first appeared in the spring of 1918, waned during the summer and then resurged from October to December, the team said.

The current H1N1 pandemic is different than in 1918, Finch cautioned.

During the current pandemic, there have been secondary infections and deaths among pregnant women. But for the 1918 flu, secondary infections were "off the scale," he said.

Influenza in pregnancy is linked to maternal complications like serious respiratory problems that could affect the fetus, said Dr. Tina Chambers, a specialist in perinatal epidemiology at the University of California at San Diego.

Public health authorities have advised pregnant women to protect themselves from swine flu by:

• Getting the H1N1 shot when it becomes available.
• Treating fever.
• Seeing a doctor promptly if they experience flu symptoms, since treatment with antivirals in the first 48 hours can reduce the severity of disease.

With files from The Canadian Press