Pregnant Women At Greatest Risk Of Flu Due To Hyperactive (Not Weakened) Immune Systems

For the past however long, mums-to-be have suffered from the flu virus worse than any other member of the public due to (what was believed to be) a weakened immune system.

However, a new health study has found that this isn't actually the case.

The immune systems of pregnant women are, in fact, hyperactive - an unexpected discovery as immune responses are thought to be suppressed by pregnancy in order to prevent a woman's body from rejecting her unborn baby.

Researcher Dr Catherine Blish, from Stanford University in the US, said: "We were surprised by the overall finding. We now understand that severe influenza in pregnancy is a hyper-inflammatory disease rather than a state of immunodeficiency.

"This means that treatment of flu in pregnancy might have more to do with modulating the immune response than worrying about viral replication."

The researchers took immune cells from 21 pregnant and 29 healthy, non-pregnant women and exposed them to different flu viruses in the laboratory.

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Cells taken from women six weeks after they had given birth were also tested.

Pregnancy boosted the immune response to swine flu, the H1N1 strain that caused a pandemic in 2009, by affecting two types of white blood cell, natural killer (NK) and T-cells.

Compared with those from non-pregnant women, both cell types produced larger amounts of signalling molecules that attract other immune cells to infection sites.

This could lead to lungs becoming clogged up by an influx of immune cells, said Dr Blish.

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7 Awesome Things Your Body Does During Pregnancy

1. Your Blood Volume Increases(01 of07)

During pregnancy, the volume of blood in a woman's body increases by a whopping 50 percent in order to help support the uterus. Accordingly, the amount of blood pumped by the heart increases as well. As the Merck Manual explains, by the end of pregnancy, a woman's uterus receives one-fifth of her pre-pregnancy blood supply. (credit:Getty)

2. You Actually Glow(02 of07)

If you find yourself looking all dewey and glow-y during your pregnancy, it's not just because you're brimming with I'm-about-to-become-a-mom sentiment; there's also a physiological basis for it. The aforementioned increase in circulation that occurs during pregnancy causes many women's faces to appear brighter, or flushed. And, as the American Pregnancy Association reports, as women's bodies produce more hormones, their oil glands can go into overdrive, resulting in that famed pregnancy glow. (credit:Getty)

3. You Grow An Entire Organ(03 of07)

During pregnancy, women's bodies grow a whole new organ, i.e., the placenta -- a structure that develops in the uterus and provides oxygen and nutrients to your growing baby (while also playing a key role in waste removal). The organ typically grows onto the upper part of the uterus and is linked to your baby via the umbilical cord. After your baby's born and the placenta's job is done, it is simply expelled through the birth canal (although some women, including a growing number of celebs, then ingest it for its reputed health benefits -- a practice known as "placentophagia"). (credit:Getty)

4. You Loosen Up(04 of07)

More specifically, as you move through your pregnancy, hormones (especially the aptly named "relaxin") help soften the ligaments that hold your bones together and the pelvic bones themselves begin moving to accommodate your baby's birth. Sometimes, this can cause a bit of pain and discomfort (if it's severe enough, you should see your doctor), although as What To Expect reports, once your baby is born, your joints will firm up again. (credit:Getty)

5. You Stop Shedding(05 of07)

Do you have the thickest, most amazing head of hair, like, ever? During pregnancy you stop shedding hair at it's normal rate. As Baby Center explains, most of the time between 85 and 95 percent of the hair on your head is growing, while the rest is in a "resting" stage, before it falls out. But during pregnancy, higher estrogen levels extend that growth phase, meaning you lose less hair and may suddenly find yourself with a gloriously thick ponytail. (Although, as we previously reported, after your baby's born, that "extra" hair will fall out.) (credit:Getty)

6. You Breathe Differently(06 of07)

It's not uncommon for pregnant women to feel short of breath, particularly later in their pregnancy when the uterus grows and begins to press on the diaphragm. But breathing also changes because of the high levels of the hormone progesterone in your body signal your brain to lower the levels of carbon dioxide in the blood, Merck explains -- yet another amazing example of all the things your body does to support and accommodate a growing baby. (credit:Getty)

7. You Become Particularly Orgasmic(07 of07)

As Babble explains, the increased blood flow to a woman's genitals -- plus the general surge in any number of hormones that influence desire -- can make many pregnant women feel libidinous. And those changes can also increase sensitivity, allowing many women to orgasm more easily. But as with all things related to sexuality, this is totally individual -- some women want nothing to do with sex while they're pregnant. (credit:Getty)

Catching flu when pregnant, especially pandemic strains, is known to heighten the potentially fatal risk of pneumonia.

Both swine flu and the seasonal flu strain H3N2 also caused NK and T-cells to be activated in a greater variety of ways in pregnant women, the researchers reported in the journal Proceedings of the National Academy of Sciences.

Lead author Dr Alexander Kay, also from Stanford University, said: "If our finding ends up bearing out in future studies, it opens the possibility that we can develop new immune-modulating treatment approaches in the setting of severe influenza, especially in pregnant women."

He hoped the research would remind women who are pregnant or planning a pregnancy to get their flu shots.

"Flu vaccination is very important to avoid this inflammatory response we're seeing," Dr Kay said. "But only 50% of pregnant women are currently vaccinated for influenza."

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