Influenza infection during pregnancy associated with increased risk of fetal death
Jan 19th – Pandemic influenza infection during pregnancy is associated with an increased risk of fetal death.
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1. Pandemic influenza infection during pregnancy is associated with an increased risk of fetal death.
2. Influenza vaccination in pregnancy does not harm the fetus and should be encouraged in pregnant women.
Influenza infection during pregnancy is linked with an increased risk of fetal death, while vaccination reduced risk of influenza and was not associated with increased risk of fetal death or unfavorable birth outcomes. Results may not be widely generalizable due to the present work’s study of outcomes from a single influenza epidemic in one country, particularly given the immense variation in severity and vaccination efficacy from year to year. However, general lessons learned, such as the safety of vaccine in pregnant women, can be applied to future epidemics. The findings of this study are particularly timely and pertinent in the setting of the current influenza epidemic, the worst outbreak in a decade.
Click to read the study in the current issue of NEJM
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1. Pandemic influenza infection during pregnancy is associated with an increased risk of fetal death.
2. Influenza vaccination in pregnancy does not harm the fetus and should be encouraged in pregnant women.
Primer: The flu is an acute respiratory infection caused by the influenza virus. It is transmitted through large particle droplets that can be spread by sneezing and coughing. The flu affects more illness in cold weather months when colder air makes viral particles less dense, allowing them to travel further into the lungs. Traditionally, the flu is characterized by the abrupt onset of fever, headache, myalgias, and malaise (systemic symptoms) often with respiratory symptoms such as non-productive cough, sore throat, and nasal discharge. In susceptible individuals, influenza can be complicated by pneumonia. Because of changes in the immune system (decreased immune response), heart (increased cardiac output), and lungs during pregnancy, pregnant women are particularly susceptible to severe complications from influenza. Moreover, contracting influenza increases risks of adverse pregnancy outcomes that can harm the fetus, such as premature labor and even fetal death. (1,4)
Influenza occurs in distinct outbreaks every year. The reason for the unique epidemiologic pattern of influenza is the virus’s ability to mutate and change its antigenic properties. Thus, vaccines are is redesigned annually to cover what virologists predict will be the  most common, virulent strains that  year, such that patients must be re-vaccinated yearly. To protect themselves and their unborn babies, the CDC recommends that all pregnant women receive the flu vaccine. While studies have found no increased risk of adverse outcomes in pregnant women who received vaccinations, anecdotal reports of increased rates of fetal deaths have raised public concern and dissuaded some women from getting vaccinated. (2,3,4)
In 2009, the H1N1 influenza pandemic was particularly severe, with unprecedented speeds of spread. Although the effects of the pandemic were devastating, they also provided an opportunity to study the spread of epidemics and the best ways to protect vulnerable populations for application in future epidemics.(5) This study set out to evaluate how the 2009 epidemic affected pregnant women and fetal outcomes. In particular, they assessed rates of fetal death and the effectiveness of vaccination in pregnant women exposed to the flu.
Background reading:
- Uptodate: Clinical manifestations of seasonal influenza in adults
- Uptodate: Epidemiology of influenza
- Uptodate: seasonal influenza vaccination in adults
- CDC: Pregnant Women and Influenza
- RMS: Learning from the 2009 H1N1 influenza pandemic
This [retrospective cohort] study evaluated pregnancy outcomes in 117,347 women during the 2009-2010 H1N1 influenza epidemic, using data from the Norwegian birth-registry. The primary outcome was fetal death, defined as any miscarriage or stillbirth after 12 weeks of pregnancy. Analysis compared the rates of fetal death in pregnant women exposed to the pandemic, clinically diagnosed with influenza (8.9%), and vaccinated against influenza (54%).
Pregnant women diagnosed with influenza experienced  an increased risk of fetal death (Hazard Ratio: 1.91, 95% CI: 1.07-3.41). In pregnant women, vaccination substantially reduced risk of influenza compared with non-vaccinated women (HR: 0.30, 95% CI: 0.25-0.34). Further, vaccination during pregnancy reduced the risk of fetal death, though not significantly (HR: 0.88, 95% CI: 0.66-1.17). There was  no association between vaccination and nonfatal birth outcomes, such as preterm birth, low birth weight, and low Apgar score.
In sum: Influenza infection during pregnancy is linked with an increased risk of fetal death, while vaccination reduced risk of influenza and was not associated with increased risk of fetal death or unfavorable birth outcomes. Results may not be widely generalizable due to the present work’s study of outcomes from a single influenza epidemic in one country, particularly given the immense variation in severity and vaccination efficacy from year to year. However, general lessons learned, such as the safety of vaccine in pregnant women, can be applied to future epidemics. The findings of this study are particularly timely and pertinent in the setting of the current influenza epidemic, the worst outbreak in a decade.
Click to read the study in the current issue of NEJM
By [MS] and [LH]
More from this author: Vulvovaginal swabs more sensitive than endocervical swabs at detecting chlamydia, Bipolar Disorder is associated with adverse pregnancy outcomes regardless of pharmacologic treatment, No-cost contraception reduces unintended pregnancies
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Maren Shapiro:Â Maren is a 2nd year M.D. Candidate at the University of Pennsylvania.
Leah Hawkins:Â Leah is a 5th year M.D./MPH candidate at Harvard Medical School.
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