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H1N1 Influenza in Pregnant Women

H1N1-infected pregnant women appear to be at increased risk for severe disease and death.

During seasonal influenza epidemics and previous pandemics, pregnancy has been associated with increased disease severity. For example, in a series of pregnant women with influenza reported during the 1918 pandemic, about half developed pneumonia, and of these women, more than half died. More recently, during the 1957 pandemic, half of the influenza-related deaths among women of reproductive age in Minnesota occurred during pregnancy. To assess the situation with the new H1N1 virus, the CDC implemented enhanced surveillance for H1N1 infections among pregnant women in the U.S.

From April 15 through May 18, 2009, 34 H1N1 cases (31 confirmed, 3 probable) from 13 states were reported in pregnant women. The women were aged 15 to 42 (median, 26); 44% were Hispanic. Symptoms were similar to those in the nonpregnant general population, except that shortness of breath was more common (risk ratio, 2.3; 95% confidence interval, 1.5–3.6). Eleven of the women were hospitalized; 6 died (4 during the third trimester), all with primary viral pneumonia and acute respiratory distress syndrome. Among those who died, one was obese, and two had other, nonsevere medical problems; three were healthy. Although all six received oseltamivir, the interval between symptom onset and first receipt ranged from 6 to 15 days (median, 9 days). The five infants born to the women who died were not infected.

Among persons with H1N1 infection, hospital admission was more common for pregnant women (32.4%; 95% CI, 17.4–50.5) than for the general population (4.2%; 95% CI, 3.7–4.8). Pregnant women accounted for 0.62% of all reported confirmed and probable H1N1 cases during the study period and 13% of deaths.

Comment: Given the potential severity of H1N1 infection (and the absence of known increases in adverse effects from oseltamivir) during pregnancy, prompt treatment of pregnant women with suspected H1N1 infection is warranted. Treatment should ideally be started 48 hours after symptom onset, but not withheld for women who have been symptomatic for >48 hours. In recent years, few pregnant women (14% in 2004 [Vaccine 2008; 26:1786]) have received influenza vaccine. Pregnant women should receive high priority for H1N1 vaccine, when it becomes available. Vaccinating pregnant women may also protect infants after birth.

— Mary E. Wilson, MD

Published in Journal Watch Infectious Diseases August 5, 2009

Citation(s):

Jamieson DJ et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet 2009 Aug 8; 374:451.

• Medline abstract (Free)

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