Adverse birth outcomes were more common in infants born to women with the flu, specifically influenza A(H1N1)pdm09, during pregnancy in the 2009 pandemic year, researchers found.
Compared with births among women without influenza A(H1N1)pdm09 that year, infants born to those who came down with that strain were more likely to be born preterm and have low Apgar scores at 5 minutes, reported Kim Newsome, MPH, of the CDC, and colleagues.
Pregnant women with 2009 H1N1 influenza who were admitted to the intensive care unit (ICU) were also at increased risk of adverse infant outcomes, including low birth-weight, the authors wrote in Birth Defects Research.
They noted that prior studies during the 2009 H1N1 pandemic found that women with severe flu admitted to the ICU were more likely to have “poor neonatal outcomes,” and the new study was done “to better understand the effects of influenza during pregnancy on infants.”
The researchers examined data from five state/local health departments with information on infants born to women with influenza A(H1N1)pdm09 from April to December 2009. Birth certificate data was examined from two comparison groups and matched based on month of conception, sex, and county of residence.
Overall, there was available data on 490 infants born to mothers with 2009 H1N1 influenza. Comparison groups included 1,451 matched singletons born during the same time period, and 1,446 matched singletons using the prior year of conception.
Women with 2009 H1N1 influenza were three times more likely than the comparison groups to be age <18 compared with age ≥35, and more than twice as likely to be black/non-Hispanic race/ethnicity compared with white/non-Hispanic race/ethnicity. However, women from comparison groups were more likely to deliver vaginally than women with 2009 H1N1 influenza were, the authors said.
Compared with infants in the same-year comparison group, those born to women with influenza A(H1N1)pdm09 were more likely to be preterm (adjusted RR 1.7, 95% CI 1.3-2.2) and to have low Apgar scores at 5 minutes (aRR 4.0, 95% CI 2.1-7.6), but were no more likely than infants in comparison groups to be born small for gestational age.
Women who were hospitalized with severe 2009 H1N1 influenza (defined as admitted to the ICU or died) were more likely than women with “less severe illness” (defined as either admitted to the hospital, but not the ICU or not admitted to the hospital) to have infants with certain adverse outcomes, including the following:
- Preterm (aRR 3.9, 95% CI 2.7-5.6)
- Low birth-weight (aRR 4.6, 95% CI 2.9-7.5)
- Apgar scores ≤6 at 5 minutes (aRR 8.7, 95% CI 3.6-21.2)
Moreover, infants delivered when researchers estimated a woman had the flu were more likely to have lower Apgar scores, preterm birth, and lower birth weight than women in comparison groups. There was also a higher risk of preterm birth for women diagnosed with 2009 H1N1 influenza in the first trimester versus comparison groups, but this was not seen in later trimesters. Despite small numbers and multiple comparisons, this finding “deserves further investigation,” Newsome and co-authors said.
They added that limitations to the data include potential unmeasured confounders, such as maternal education and comorbid conditions such as maternal obesity and diabetes.
Taken together, the findings “support the importance of influenza vaccination among pregnant women and the importance of antiviral treatment as early as possible for pregnant women to avert severe illness,” the researchers concluded.
The authors reported having no conflicts of interest to declare.