Babies born between April and July are more likely to have a certain heart defect, doctors reported on Monday, and they believe a common infection such as strep throat may play a role.
The condition, called hypoplastic left heart syndrome, affects the entire left side of the heart and usually requires at least three operations to reconstruct it.
Dr. Pirooz Eghtesady and colleagues at Cincinnati Children's Hospital in Ohio studied 1,500 newborns from 38 children's hospitals in the United States who had left-sided congenital heart diseases between 1996 and 2006.
They found a clear seasonal pattern to hypoplastic left heart syndrome but not other diseases, they told a meeting of the American College of Cardiology in Orlando.
"Strong seasonality is a clue that environmental factors may play an important role in this disease, as we see, for example, with such common childhood illnesses as asthma and croup," Eghtesady said in a statement.
They are now conducting a study to see whether strep throat, an infection caused by Streptococcus bacteria, may be to blame. Untreated infections of this strain of strep cause rheumatic fever, and sometimes lifelong heart disease.
Strep throat is more common in the winter months and may affect a developing fetus.
Studies have suggested that the body's immune response to strep can damage the left side of the heart. Eghtesady said preliminary evidence suggests that many mothers whose newborns had left-sided heart injury had a significant history of problems related to strep throat.