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FRIDAY, Dec. 19 (HealthDayNews) -- Here's more reason for mothers-to-be to take special precautions this flu season.

A new study finds women who have a fever during the second trimester of pregnancy are more likely to give birth to children who develop behavioral and psychological disorders.

"It's the first study to look at fever with respect to psychological and behavioral outcomes," says lead author Stefan Dombrowski, an assistant professor of graduate education at Rider University in Lawrenceville, N.J.

"If moms do happen to get sick, it's important to be aware of elevated fever and try to control that," he adds. The study appears in a recent issue of Birth Defects Research.

Unlike rubella or chicken pox, influenza does not appear to cross the placenta and harm the baby, Dombrowski explains. He and his colleagues suspected that some other disruption, such as fever, might be causing psychological and behavioral problems in children because that period of a woman's pregnancy is critical for fetal central nervous system development.

To find their answer, the authors turned to data from a Finnish study of early childhood temperament. The sample consisted of 6,401 children born between July 1, 1975, and June 30, 1976, in Helsinki and its adjacent suburbs. After eliminating data for one twin of each twin pair, the final sample included 6,388 children.

The study compares outcomes at 6 months, 5 years and 12 years for children whose mothers never reported fever in pregnancy and children whose mothers reported fever in the second and third trimesters.

The findings demonstrate a connection between second trimester fever and various measures of temperament, behavior and academic performance.

Six-month-old infants had a much greater chance of becoming more distressed around new situations or strange adults if their mothers had fever in the second trimester than babies born to moms who didn't report fever.

Five-year-olds of moms who had second trimester fever could not attend to play and learning materials as long as their peers and were more socially inhibited in the presence of strange adults or children.

At age 12, children of moms with second trimester fever were significantly more likely to have trouble focusing on tasks and were at greater risk for reduced academic achievement than their peers.

One important caveat: the mothers in the study reported either having or not having fever since their last monthly visit to a prenatal clinic. The data did not reflect the fevers duration or intensity.

In a commentary appearing in the same journal, Assistant U.S. Surgeon General Dr. Jose Cordero, director of the government's National Center on Birth Defects and Developmental Disabilities, says the study raises "an interesting hypothesis" but notes that more research is needed to better understand the causes of behavioral outcomes in children.

The National Institutes of Health in partnership with the U.S. Centers for Disease Control and Prevention has proposed a National Children's Study that may help identify some of the common factors that lead to learning disabilities, attention-deficit disorder, and other developmental conditions, he writes.

Dr. Owen Montgomery, an associate professor of clinical obstetrics and gynecology at Drexel University College of Medicine in Philadelphia, cautions that a connection between second-trimester flu and developmental difficulties has not been shown in research published in major clinical journals.

"I have concerns about worrying unnecessarily 4 million pregnant women in this season of cold and flu that they would then be dooming their children to psychological damage in the rest of their lives," he says.

Women who are pregnant should get a flu shot, exercise, eat a healthy diet, get plenty of rest and practice proper hygiene, Montgomery advises. But they should not panic if they feel a cold or flu coming on, he adds.

"Women are going to get the flu, and if they're sick, they can absolutely call their doctor or midwife," he says.

More information

Learn more about developmental disabilities from the National Center on Birth Defects and Developmental Disabilities. The University of Michigan Health System has more on the flu and pregnancy.

(SOURCES: Stefan Dombrowski, Ph.D., assistant professor, graduate education, Rider University, Lawrenceville, N.J.; Owen Montgomery, M.D., associate professor, clinical obstetrics and gynecology, Drexel University College of Medicine, Philadelphia; November 2003 Birth Defects Research (Part A) )

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