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Pregnancy and the Flu

Pandemic H1N1 and seasonal influenza take their toll on pregnant women; vaccination is a top priority.

Mortality among pregnant women was relatively high during the 1918 and 1957 influenza pandemics. Now, CDC investigators have reported hospital admission rates among pregnant women with confirmed or probable pandemic H1N1 ("swine") flu. Of 34 pregnant women with H1N1 influenza infection, 11 (32%) were admitted to the hospital for 2 to 15 days; of these women, 3 were admitted to the intensive care unit, and 1 died. This hospital admission rate is four times higher than that in the general population. Moreover, of 45 people who died from pandemic H1N1 influenza from April 15 to June 16, 2009, 6 (13%) were pregnant women (age range, 20–33) who were otherwise healthy. Five of these women had viable pregnancies and underwent cesarean deliveries; no infants had evidence of influenza infection.

Seasonal influenza also takes its toll on pregnant women (especially during the third trimester), although the proportional increase in morbidity is not as great as with pandemic H1N1. Seasonal influenza vaccination is recommended by the CDC and the American College of Obstetricians and Gynecologists for all pregnant women. However, only 15% of pregnant women receive the vaccine. Key barriers to more-widespread vaccination are general hesitance of pregnant women to receive medical products and difficulties associated with administering vaccines in obstetricians' offices. When the seasonal influenza vaccine becomes available this fall, it should be administered to pregnant women according to routine recommendations.

A vaccine against pandemic H1N1 influenza is not yet available. Because preexisting immunity is lacking, two doses will be required. The CDC's recommended order of priority for pandemic H1N1 vaccination is as follows: (1) pregnant women; (2) household contacts and caregivers of children younger than 6 months; (3) healthcare and emergency service workers; (4) all children, adolescents, and young adults (age range, 6 months–24 years); and (5) adults (age range, 25–64) who have underlying medical conditions (such as heart disease, respiratory illness, or diabetes) or who are immunocompromised.

Comment: The five groups with the highest priority for H1N1 vaccination account for about 50% of the U.S. population. The challenge will be producing and delivering enough vaccine. In the meantime, the CDC recommends that pregnant women who contract H1N1 influenza be treated with oseltamivir (Tamiflu; JW Womens Health May 18 2009).

— Anna Wald, MD, MPH

Published in Journal Watch Women's Health August 6, 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)

MacDonald NE et al. Influenza immunization in pregnancy. Obstet Gynecol 2009 Aug; 114:365.

• Medline abstract (Free)

Phillippe M. Pandemic influenza: What obstetricians need to know. Obstet Gynecol 2009 Aug; 114:206.

• Medline abstract (Free)

CDC advisors make recommendations for use of vaccine against novel H1N1 [press release]. Atlanta, GA: Centers for Disease Control and Prevention (CDC); Jul 29 , 2009. (http://www.cdc.gov/media/pressrel/2009/r090729b.htm)