The pandemic of 2009 is reminding us of something we’ve known for some time; that novel influenza viruses take a heavy toll among pregnant women and their unborn children.
Today, we’ve some new research regarding those born during the 1918 pandemic, but first, a review of some earlier studies.
Researchers know that during the 1918 pandemic an abnormally high number of pregnant women died from the influenza, and those that survived endured a very high miscarriage rate.
Even during the much milder 1957 Asian Flu, pregnant women reportedly suffered disproportionately higher mortality rates than non-pregnant women of the same age.
In a Perspective, written by 3 CDC physicians (Sonja A. Rasmussen, Denise J. Jamieson, Joseph S. Bresee) and published in the CDC Journal of EID article, Pandemic Influenza and Pregnant Women in February of 2008, we get this assessment of the historic impact of influenza on pregnant women.
Although appropriate nonpregnant control groups were generally not available, mortality rates among pregnant women in the pandemics of 1918 and 1957 appeared to be abnormally high (5,7). Among 1,350 reported cases of influenza among pregnant women during the pandemic of 1918, the proportion of deaths was reported to be 27% (5).
Similarly, among a small case series of 86 pregnant women hospitalized in Chicago for influenza in 1918, 45% died (6). Among pregnancy-associated deaths in Minnesota during the 1957 pandemic, influenza was the leading cause of death, accounting for nearly 20% of deaths associated with pregnancy during the pandemic period; half of women of reproductive age who died were pregnant
And during the opening months of the 2009 pandemic, we’ve seen a 4 to 6 fold increase in influenza-related hospitalizations among pregnant women compared to the rest of the population. Sadly, we’ve received reports of numerous fatalities as well.
All of which has led doctors to advise that pregnant women receive antiviral treatment if infected, and be targeted for early vaccination when that becomes available.
One aspect of influenza infection during pregnancy that has been getting less attention, simply because the impact may not be as obvious or immediately apparent, are the effects prenatal exposure to the virus may have on the fetus.
There have been studies in the past that have linked such exposure to developmental problems, although the evidence is indirect. Once again, the authors of the EID Perspective weigh in:
Although certain infections are well recognized to increase the risk for adverse pregnancy outcomes, the effects of maternal influenza infection on the fetus are not well understood. Viremia is believed to occur infrequently in influenza (18), and placental transmission of the virus also appears to be rare (19).
However, even in the absence of fetal viral infection, animal studies suggest that adverse effects can still occur. Prenatal influenza infection in the mouse has been associated with histopathologic changes in the brain (20) and behavioral alterations (21) in offspring. Although influenza virus RNA has not been detected in the fetal brain, these changes suggest that fetal effects could be secondary to the maternal inflammatory response, rather than the result of a direct viral effect (22).
In other words, it may not be so much the virus, but the immune response mounted by the mother, that can cause fetal damage. Again they write:
Associations between maternal influenza infection and childhood leukemia (23), schizophrenia (24), and Parkinson disease (25) have been suggested by some studies. Even if the influenza virus does not have a direct effect on the fetus, fever that often accompanies influenza infection could have adverse effects.
In April of this year, just days before the news of the novel H1N1 virus made the headlines, news of another retrospective study emerged reporting lower IQ scores (on a population basis) among those born during the Hong Kong Flu Pandemic.
A new study found that early prenatal exposure to the Hong Kong flu may have interfered with fetal cerebral development
Oslo, Norway – April 15, 2009 – The Hong Kong flu pandemic was responsible for more than 700,000 deaths worldwide in the late 1960s, with major disease outbreaks in Europe in the winter of 1969-1970.
A number of studies have been conducted to determine if prenatal exposure to the influenza virus may result in mental disorders that affect a small portion of the population, but no studies have explored the possible effects of prenatal exposure on the mean intelligence in the general population. A new study found that early prenatal exposure to the Hong Kong flu may have interfered with fetal cerebral development and caused reduced intelligence in adulthood. The study is published in Annals of Neurology.
The upshot of this study is that military IQ tests conducted on those born in the years just before, during, and after the 1968 Hong Kong flu pandemic indicate a lowering of test scores for those born during the height of the pandemic.
All of which sets the stage for a new report, just released, that looked at the long-term cardiovascular history of those born during the 1918 Spanish flu, and found a heightened level of heart disease 60 years later.
Men exposed to H1N1 strain while in utero also shorter than peers born months before or months after 1918 pandemic, study finds
People exposed to a H1NI strain of influenza A while in utero were significantly more likely to have cardiovascular disease later in life, reveals a new study to be published in Journal of Developmental Origins of Health and Disease on Oct. 1.
"Our point is that during pregnancy, even mild sickness from flu could affect development with longer consequences," said senior author Caleb Finch, USC professor of gerontology and biological sciences.
Interestingly, the military discovered during WWII that men born in 1919 were likely to be slightly shorter than men born in the years before and after the Spanish flu.
While none of these studies appear to prove a definitive link between prenatal exposure to the virus and developmental problems later in life, there does appear to be enough evidence here for a heightened concern.
All of which highlights the need for pregnant women to contact their doctors if they suspect that they may have the H1N1 influenza, and to avail themselves of the flu vaccine as soon as it becomes available.
The HHS has a video on Youtube regarding their advice for pregnant women.
- Secretary Kathleen Sebelius, HHS
- Tina Chin, White House Council on Women
- Rear Admiral Anne Schuchat, CDC
- Dr. Tony Fauci, National Institutes of Health/NIAD
- Dr. Laura Riley, OB/GYN - Mass General Hospital
- Tina Johnson, American College of Midwives