Could the flu shot cause miscarriage or stillbirth?

I don’t think there’s anything more frustrating than not knowing why Ada died. Unfortunately we are not alone in not knowing. In a lot of cases, no reason is found – up to 50% of all stillbirths where an autopsy is performed, and when the tests aren’t done the majority of stillbirths are unexplained. Even a higher number of miscarriages are unexplained. We grasp at anything we can think of – did I drink too much caffeine? did I sleep on my back too long? maybe I didn’t eat enough protein? – in hopes of figuring out what happened so we can avoid losing another child.

Now that obstetricians are recommending that every pregnant woman get the flu shot (along with the CDCMayo Clinic, and others), it’s easy to think “I got the flu shot and lost the baby”. While I can totally understand that, there’s a lot of things that we all do that certainly don’t cause miscarriage or stillbirth even though there’s a high correlation. For example, most women eat saltines and drink ginger ale while pregnant, so most of us that experience miscarriage or stillbirth had eaten saltines and drank ginger ale. Of course that doesn’t mean our loss was caused by those things!

To make things more confusing, very few medicines or vaccines are tested directly on pregnant women or babies. It’s a difficult debate (Lancet, Healthline) where the need for information is pitted against the need to protect developing babies. Thankfully there are more and more studies of the flu vaccine in pregnant women all the time, but  they are more rare than studies in non-pregnant adults. So, many vaccines are untested in pregnant women.

Vaccines often end up in pregnancy drug category B or C because the only safety evidence is from studies in pregnant animals. What does this mean? If a vaccine is in category B or C it means we just don’t have enough information. This does not mean there’s evidence it’s unsafe (that’s category D or X). Thankfully, scientists have followed up with studies of pregnant women.

A recent example of a huge study is Risk of Fetal Death after Pandemic Influenza Virus Infection or Vaccination, published in January of 2013. The researchers (funded by the Norwegian Institute of Public Health and the US National Institutes of Health) looked at 117,347 pregnancies in Norway from 2009-2010. Of all these pregnancies, 570 babies were miscarried or stillborn (4.9 deaths per 1000 births – for comparison the US has 6.25 stillbirths per 1000 plus however many miscarriages).

Among women got the flu vaccine, women who had the flu during pregnancy were more likely to lose the baby compared to women who did not have the flu. Among women who did not get the flu, women who had the vaccine were less likely to lose the baby than women who were not vaccinated. Today Health has a nice summary of this study: Flu vaccine safe in pregnancy, study confirms.

Another way to look at potential problems with vaccines is to look for any potential adverse reactions that could be related to taking a medication. The CDC collects such data in the Vaccine Adverse Event Reporting System (VAERS). Adverse events reported in pregnant women were described in the study Adverse events in pregnant women following administration of trivalent inactivated influenza vaccine and live attenuated influenza vaccine in the Vaccine Adverse Event Reporting System, 1990-2009.

Between 1990 and 2009, there were only 20 miscarriages or stillbirths reported by pregnant women who had taken either inactivated or live attenuated flu vaccines. This means there were just 1.9 miscarriages or stillbirths per million pregnant women vaccinated ( again, for comparison, the US has 6.25 stillbirths per 1000 plus however many miscarriages).

Between these two huge studies, it’s clear that the flu vaccine has a protective effect, with far fewer miscarriages and stillbirths in women who are vaccinated than in women who are not.

Of course, these aren’t the only studies that found the flu vaccine to be safe – you can find a ton more at PubMed. One great thing is that More types of flu shots available this year than ever so we can pick and choose the ones that we feel most comfortable with, based on the latest research.

References

Håberg S.E., Trogstad L., Gunnes N., Wilcox A.J., Gjessing H.K., Samuelsen S.O., Skrondal A., Cappelen I., Engeland A. & Aavitsland P. (2013) Risk of Fetal Death after Pandemic Influenza Virus Infection or Vaccination, New England Journal of Medicine, 368 (4) 333-340. DOI:

Moro P.L., Broder K., Zheteyeva Y., Walton K., Rohan P., Sutherland A., Guh A., Haber P., DeStefano F. & Vellozzi C.(2011) Adverse events in pregnant women following administration of trivalent inactivated influenza vaccine and live attenuated influenza vaccine in the Vaccine Adverse Event Reporting System, 1990-2009, American Journal of Obstetrics and Gynecology, 204 (2) 146.e1-146.e7. DOI:

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One thought on “Could the flu shot cause miscarriage or stillbirth?

  1. richiesbabe says:

    thank you for this very informed report. i got my flu shot pregnant recently…and you’re always filled with such doubt because of all of the social media/but usually lack-of-researched people out there that make you feel extreme paranoia. we also have a son that was born early and gets the flu shot each year. btw—i have just been through your entire site. i am so sorry for your loss. there are no words.
    my daughter’s name in polish is ada (but pronounced perhaps differently—a as in alligator + da as in duh). and we lost a baby at the end of our first trimester in 2010. our son was a hard fought battle to get here, and now i am pregnant again but went through plenty of emotions of fear—much like you mentioned in your most recent article about proper care.
    you are a wonderful mommy…my sorrow for your loss truly has no words.
    here are the two articles that i wrote on the subject. truly…words are difficult.
    many hugs,
    brooke
    http://wp.me/p3Bh9m-6B My nose ring was snot a good idea…and we got a puppy
    and
    http://wp.me/p3Bh9m-y2 October: national pregnancy and infant loss

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