Novel Influenza H1N1 has Dramatic Risks for Pregnant Women

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Like previous epidemic and pandemic diseases, 2009 pandemic influenza A (H1N1) may pose an increased risk of severe illness in pregnant women. To see if there were clinical experiences that matched this assumption a Californian investigation by their Department of Health reviewed demographic and clinical data reported from April 23 through August 11, 2009, for all H1N1-infected, reproductive-age women who were hospitalised or died. These included non-pregnant women, pregnant women, and postpartum women (those who had delivered ≤2 weeks previously).[1]

A total of 10% of the 1088 patients who were hospitalised with or died from 2009 H1N1 influenza, as reported to the California Department of Public Health (CDPH), were pregnant, the rate of hospitalisation among pregnant women was approximately four times the rate in the general population.[2]

Defining Inclusion Criteria

A review of all pregnant, postpartum, and non-pregnant case patients of reproductive age (15 to 44 years of age) was performed. Pregnant patients were those who were pregnant at the time of onset of influenza symptoms. Postpartum patients were those with an onset of influenza symptoms during the first 2 weeks after delivery. For pregnant and postpartum patients who were admitted to an intensive care unit (ICU) while ill, an obstetrician–gynaecologist from the research team contacted health care providers when possible to obtain additional detailed information about complications during delivery and the course of the maternal illness.

Data Collection

From April 23 through August 11, 2009, data were reported for 94 pregnant women, 8 postpartum women, and 137 non-pregnant women of reproductive age who were hospitalised with or died from 2009 H1N1 influenza, for a total of 239 women in this age group. Dates of symptom onset ranged from April 3 to August 5, 2009. In all, 41 local health jurisdictions accounting for 96% of the population of California reported cases to the CDPH: 19 jurisdictions accounting for 79% of the population reported pregnant and postpartum cases, and 27 jurisdictions accounting for 86% of the population reported non pregnant cases.

Of the 94 pregnant patients, 5 (5%) were in the first trimester, 35 (37%) were in the second trimester, and 54 (57%) were in the third trimester. There were two spontaneous abortions and 35 deliveries: 3 in the second trimester (range, 25 to 28 weeks’ gestation) and 32 in the third trimester. Two women delivered twins. Approximately one third (32 of 93 [34%]) had established risk factors for complications from influenza other than pregnancy.

Outcome Results

As compared with early antiviral treatment (administered ≤2 days after symptom onset) in pregnant women, later treatment was associated with admission to an intensive care unit (ICU) or death (relative risk, 4.3). In all, 18 pregnant women and 4 postpartum women (total, 22 of 102 [22%]) required intensive care, and 8 (8%) died. Six deliveries occurred in the ICU, including four emergency cesarean deliveries. The 2009 H1N1 influenza–specific maternal mortality ratio (the number of maternal deaths per 100,000 live births) was 4.3.


2009 H1N1 influenza can cause severe illness and death in pregnant and postpartum women; regardless of the results of rapid antigen testing, prompt evaluation and antiviral treatment of influenza-like illness should be considered in such women. The high cause-specific maternal mortality rate suggests that 2009 H1N1 influenza may increase the 2009 maternal mortality ratio in the United States.


The risks linked to pregnancy are attached to altered innate immune responses that are adjusted by the mother to prevent rejection of foreign DNA from the father. The consequence of this, as in most influenza virus assaults, is that pregnant women are immunologically more vulnerable.[3] In summary a variety of cardiac, respiratory, hormonal, and immunologic changes that occur during pregnancy may contribute to the increased risk of influenza-related morbidity and mortality among pregnant women.[4]

The paper has elements of data collection that may require further evaluation, as time and financial constraints as well as medical pressure may contribute to either under or over reporting of H1N1 and pregnancy and post partum infection.

The role of natural agents to support the innate immune system may be considered, but should exclude herbs, because of the risk of complications. The mucosal immune support programme can be viewed as a practical approach to supporting innate immune defences to limit the risk of viral invasion.

The use of vaccination remains a controversial area in the non medical fraternity, and even in the medical community there has been considerable reluctance to explore mass vaccination. Vaccination in the pregnant women makes basic immunological sense, but may not yet meet the level of safety assurances that will make pregnant women willing to receive a relatively untested vaccine. If this is the case the use of natural agents, may make a suitable choice to allow the mothers to be to feel they are contributing to their innate immune systems natural defences, with a very good risk to benefit ratio. In addition the judicious use of effective masks when travelling or in the company of infected people will also greatly reduce – by up to 90% the chance of infection.


[1] Janice K. Louie, M.D., M.P.H., Meileen Acosta, M.P.H., Denise J. Jamieson, M.D., M.P.H., Margaret A. Honein, Ph.D., M.P.H., for the California Pandemic (H1N1) Working Group. Severe 2009 H1N1 Influenza in Pregnant and Postpartum Women in California. Published at December 23, 2009 (10.1056/NEJMoa0910444) View Abstract

[2] Jamieson DJ, Honein MA, Rasmussen SA, et al. H1N1 2009 influenza virus infection during pregnancy in the USA. Lancet 2009;374:451-458. View Abstract

[3] Harris JW. Influenza occurring in pregnant women. JAMA 1919;72:978-980. View Full Paper

[4] Jamieson DJ, Theiler RN, Rasmussen SA. Emerging infections and pregnancy. Emerg Infect Dis 2006;12:1638-1643. View Abstract

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