Women who get a seasonal flu vaccine during pregnancy may be much less likely to have a stillborn baby than unvaccinated mothers, a recent Australian study suggests.

Researchers examined data on about 53,000 women who didn’t get the vaccine during pregnancy and almost 5,100 who did. With the inoculation, women were 51 per cent less likely to have a stillborn infant.

The risk of stillbirth is still quite small – just 377 occurred in the entire study population, the equivalent of about 6.5 in every 1,000 births.

But the results suggest this inoculation may help babies thrive in the womb, said lead study author Annette Regan of the Western Australia Department of Health and the University of Western Australia in Perth.

“Pregnant women should be reassured that flu vaccine does not increase the risk of poor birth outcomes for the baby and in fact, getting a flu shot during pregnancy can reduce their risk of having a stillbirth,” Regan said by e-mail.

Scientists aren’t certain how vaccination might protect against stillbirth, Regan added. Because flu during pregnancy is associated with stillbirths, however, it’s likely that inoculation reduces the odds of flu infection for the mothers.

Even though doctors recommend that pregnant women get flu shots to protect themselves and their growing babies, less than half of mothers do, Regan and colleagues note in the journal Clinical Infectious Diseases. Often, women mistakenly fear the shots are unsafe for their babies.

When pregnant women get the flu, they’re much more likely to have complications such as preterm labor and premature births. If they get the flu early in pregnancy, it can lead to birth defects.

While pregnant women aren’t supposed to get the inhaled vaccine FluMist (MedImmune), shots are safe during pregnancy.

To explore the influence of vaccination on stillbirths, Regan and colleagues reviewed data on 58,000 births between April 2012 and December 2013.

Pregnancy losses after at least 20 weeks of pregnancy were counted as stillbirths, not miscarriages. Pregnancy typically lasts about 40 weeks and babies born after 37 weeks are considered full term.

Overall, slightly less than 9 per cent of the women in the study received flu shots during pregnancy.

Women were more likely to get flu shots if they were older and wealthier, or if they had pre-existing medical problems or developed complications such as high blood pressure or diabetes during pregnancy.

Almost half of the vaccinated women got shots during the second trimester of pregnancy, while about 19 per cent received inoculations sooner and 36 per cent got shots later in pregnancy.

There were 5 stillbirths for every 100,000 combined days of pregnancy among women who didn’t get vaccinated, compared with 3 stillbirths for every 100,000 pregnancy-days for vaccinated women.

The biggest reduction in stillbirths was seen for babies born just after the end of influenza season, when vaccination was linked to 67 per cent lower odds of it happening.

One limitation of the study is that researchers relied on women’s healthcare providers to report vaccinations to a government registry, which is optional, the authors note. This may have meant some women considered unvaccinated in the analysis actually did receive flu shots.

Researchers also didn’t have enough data on vaccinated women in the study to determine how the timing of flu shots during pregnancy might influence the odds of stillbirth, the authors point out.

Stillbirths happen in less than 1 per cent of pregnancies and are often caused by the placenta separating away from the uterine wall before delivery, a complication known as placental abruption, or by genetic abnormalities.

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4 thoughts on “Flu vaccine during pregnancy may help reduce stillbirths, study suggests

  1. Peggy’s Point Wait for it- the anti-vaxxers will be all over this one.
    I am going to make a cup of tea and watch the fun….

  2. Just more bad scientific research.

    A difference of 2 out of 100,000 combined days of pregnancy and flu vaccines are suddenly being hailed a cure for stillbirths?

  3. WestToEastCanadian
    Can anyone explain why the measure was stillbirths per pregnancy days and not per pregnancy.

    If we had 4 women in each group (Vac and Non-Vac).
    Non-Vac – 2 Stillbirths at 20 weeks (140 days), 2 Live Births Full-term (280 days)
    Vac – 1 Full-term Stillbirth at 40 weeks, 3 Full-term Live Births (280 days)

    Non-Vac – 2 Stillbirths per 840 days
    Vac – 1 Stillbirth per 1,120 days

    Standardize to 1,000 days

    Non-Vac: 2.4 Stillbirths per 1,000 pregnancy days
    Vac: 0.9 Stillbirths per 1,000 pregnancy days

    It looks like my risk is 2.7x higher in the Non-Vac group when in fact it is 2x higher. As someone who has had 2 live births and one loss my focus is on the delivery on a living child and the risks that that outcome won’t occur. Stillbirths per pregnancy days weights an earlier loss more than a later loss by reducing the denominator. This seems very odd to me and I’d love to know the logic behind using it.

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