(Reuters Health) - Pregnant women so sick with influenza that they’re admitted to the intensive care unit (ICU) are more likely to have premature and underweight babies than expectant mothers with milder flu and those who don’t catch flu at all, a recent study suggests.

Researcher compared birth outcomes for 490 pregnant women in five states who contracted the H1N1 strain of influenza-A in 2009, as well as 1,451 women without the flu who gave birth that year and 1,446 women without flu who gave birth the previous year.

Compared to women who either didn’t get the flu or had mild cases, women admitted to the ICU with severe H1N1 infections were almost four times more likely to have premature babies and more than four times as likely to have underweight infants, the study found.

Women admitted to the ICU were also more than eight times as likely to have babies with low Apgar scores, an assessment of overall wellbeing done right after birth.

“This study supports data from previous studies that have shown increased risks for infants born to pregnant women who are severely ill with flu,” said lead study author Kim Newsome of the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta.

Severe flu infections in pregnant women are generally rare. But the increased risk they present for these poor health outcomes in babies highlights the importance of vaccinating pregnant women against the flu and treating their flu cases with antivirals early to avert severe illness, the study team writes in Birth Defects Research.

Among women in the study with confirmed or suspected flu infections, 82 were so sick they were admitted to the ICU or died. Another 338 were hospitalized, but not in the ICU, and 70 were not hospitalized. Except for the 82 severe cases, none of the women with less-severe flu had higher rates of poor birth outcomes compared to women without flu.

This isn’t surprising. But it offers fresh insight into how the illness can impact birth outcomes, Newsome said by email.

“The first and most important step for pregnant women and those who might be considering pregnancy to reduce their health risks and risks to their infants is getting a flu shot,” Newsome said. “In addition, it’s important for pregnant women to get prompt treatment with antiviral medications if they get sick.”

Other everyday things like handwashing, avoiding close contact with sick people, and cleaning and disinfecting surfaces where germs can lurk can also help slow the spread of germs that cause respiratory illnesses like the flu, Newsome advised.

The flu virus spreads from person to person through droplets from coughing, sneezing or talking close to infected individuals, and can be picked up from surfaces like doorknobs where these droplets can linger, according to the CDC.

Symptoms can include fever, cough, sore throat, runny or stuffy nose, aches and pains, headaches, chills and fatigue. While most people with the flu can recover without medical treatment, some people develop serious complications that require hospitalization. Pregnant women, infants, the elderly, and people with certain chronic medical problems are particularly vulnerable to flu complications.

Beyond its small size, other limitations of the study include the lack of data on individual patient characteristics like income and education that can impact birth outcomes, the researchers note.

The study also didn’t adjust results based on whether women had obesity or diabetes, which can both increase the risk of preterm and underweight babies and make people more likely to experience serious complications from influenza.

Even so, the findings underscore the importance of vaccination, said Dr. Julie Shakib, a pediatrics researcher at the University of Utah in Salt Lake City who wasn’t involved in the study.

“The best defense against influenza is for pregnant women to get the flu vaccine as soon as soon as it is available,” Shakib said by email.

This is the best tool a pregnant mother has against influenza during pregnancy and improves her likelihood of delivering a healthy infant, Shakib added. For optimal protection against influenza after pregnancy, parents and caregivers should get vaccinated every year, as should all babies six months and older.

SOURCE: bit.ly/2HFMeSl Birth Defects Research, online January 15, 2019.