Friday, March 19, 2010

BMJ Study: Pregnancy & Flu




# 4448



One of the stories we’ve been long following (even before the outbreak of novel H1N1) has been the relationship between influenza and pregnancy.   


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.


The following anecdotal reports come from:


Rasmussen SA, Jamieson DJ, Bresee JS. Pandemic influenza and pregnant women. Emerg Infect Dis [serial on the Internet]. 2008 Jan [date cited].

Available from


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 (7).


Pregnant women also appear to be more susceptible to influenza than non-pregnant women, although the exact reasons for this aren't understood.


It is believed, however, that the normal protections of a woman's immune system are temporarily altered to allow her to carry what is essentially a foreign body- a fetus - without rejection.


While the impact of the pandemic of 2009 has been (thankfully) less than that seen with the 1957 Asian Flu, pregnant women have been hit disproportionately hard by this virus.


Last summer, it was widely reported (see Pregnancy & Flu: A Bad Combination) that pregnant women were up to 6 times more likely to be hospitalized with influenza than were non-pregnant women. 


As more time passes since the emergence of the novel H1N1 virus, new and more complete studies are released.   Our knowledge is refined, supplemented, and hopefully improved.


Today we’ve a new study that appears in the BMJ, entitled:


Critical illness due to 2009 A/H1N1 influenza in pregnant and postpartum women: population based cohort study

BMJ 2010;340:c1279

Objective To describe the epidemiology of 2009 A/H1N1 influenza in critically ill pregnant women.

Conclusions Pregnancy is a risk factor for critical illness related to 2009 H1N1 influenza, which causes maternal and neonatal morbidity and mortality.



This study indicates that the risks of influenza death among pregnant women was actually higher than first estimated last summer. I’ve lifted a few excerpts from the DISCUSSION section of this research, but please, follow this link to read the article in its entirety.




Pregnancy is a risk factor for 2009 H1N1 related critical illness. Of the 64 pregnant and postpartum women who were admitted to an intensive care unit in Australia and New Zealand with confirmed 2009 H1N1 infection, the risk of critical illness was much greater later in the pregnancy, at over 13 times the risk in the non-pregnant population. 2009 H1N1 infection was associated with substantial maternal and perinatal morbidity and mortality.


Our results show that indigenous pregnant women in Australia and New Zealand were at higher risk of critical illness due to 2009 H1N1 influenza than non-indigenous pregnant women, consistent with the observation that women from indigenous populations are at higher risk for a variety of complications of pregnancy associated with poor maternal and neonatal outcomes.20 21 22


Over half of the women had a coexisting illness. Pre-existing asthma occurred in 21% of these women compared with 12% in the general Australian birthing population.23 Among the critically ill women, 42% had a body mass index of more than 30 and 22% of more than 35; the corresponding proportions in the Australian birthing population are 24% and 10%.24 This is consistent with a preliminary report that identifies obesity as a risk factor for 2009 H1N1 related critical illness in pregnant women in the United Kingdom.2


For those with access to the full contents of the BMJ, there is an accompanying editorial by Stephen E Lapinsky, associate professor of medicine.



Critical illness as a result of influenza A/H1N1 infection in pregnancy

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