Children of women infected with influenza during pregnancy have a substantially higher risk of heart disease late in life, according to a study published on Wednesday.
The findings underscore the danger facing pregnant women from the H1N1 swine flu virus, or any other strain of flu, and also demonstrate that what happens in the womb can affect a person decades later.
Caleb Finch of the University of Southern California and colleagues studied records from the 1918 flu pandemic and found that boys whose mothers were infected during the second or third trimester of pregnancy with them had a 23 percent greater chance of having heart disease after age 60 than boys whose mothers were not infected.
Girls exposed in the second or third trimesters were not at greater risk for cardiovascular problems. But girls infected during the first trimester were 17 percent more likely than the general population have heart disease later in life.
Boys whose mothers had flu while pregnant were also more likely to be slightly shorter than their peers, Finch's team reported in the Journal of Developmental Origins of Health and Disease.
The researchers examined records of more than 100,000 people born around the time of the 1918 flu outbreak in the United States. They also examined the height of 2.7 million men born between 1915 and 1922, using military enrollment records from World War II.
Results showed that average height increased every successive year except for the period coinciding with fetal exposure to the flu pandemic.
Pregnant women are among the most vulnerable to severe complications from flu infection and have been moved to the front of the line for vaccines against the new H1N1 pandemic influenza virus.
But fewer than 25 percent of pregnant women get vaccinated for seasonal flu, according to government statistics. Health officials and groups representing doctors, nurses and other health advocates are urging that women who are pregnant get immunized against H1N1 and seasonal flu and contact their doctors if they start to develop symptoms.
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 said.
The H1N1 swine flu, which surfaced in North America in March, is a distant relative of the 1918 H1N1 strain that is estimated to have killed 50 million people and infected one-fifth of the world's population