How the immune system changes during pregnancy

As a pregnant mother, you have a higher chance of developing complications if you get flu (1)(2). Even if you are generally healthy, changes in your immune system and lung function during pregnancy make you more likely to become severely ill with the flu – and you might even need admission to hospital (2).

Possible complications include bronchitis, which can develop into pneumonia (3). You might also be more susceptible to ear and blood infections, which can lead to septic shock, as well as meningitis and encephalitis (inflammation of the brain) (3).

Flu caught during pregnancy can also be harmful to a pregnant mother’s unborn baby. Problems related to catching the flu during pregnancy include your baby being born too early or with a low birth weight (1)(3). In serious cases, it can even lead to stillbirth (1)(3).

What happens to your immune system during pregnancy?

Your immune system is well-prepared to defend against infection during pregnancy: some immune cells respond more strongly to viral challenges while other immune responses are down-regulated (4). Enhancing certain parts of your immune system during pregnancy while dampening others allows you to grow and protect the fetus inside you (5).

In fact, a successful pregnancy relies on finely tuned immune adaptations that support the growth and development of your baby during the three stages of your pregnancy (4)(5):

  • During the first trimester, a strong inflammatory system reaction (pro-inflammatory state) is needed to implant the embryo in the uterine wall (4)(5)(6).
  • A dampened inflammatory system reaction (anti-inflammatory state) during the second trimester is helpful for the growth of the baby (4)(5).
  • During the third trimester, another strong inflammatory system reaction prepares for childbirth (4)(5).


An overly strong immune response

We’ve seen how your immune system is in a ‘pro-inflammatory’ state during the first and third trimesters of your pregnancy (4). This potent immune response doesn’t necessarily work in your favour(6). Pregnant mothers’ overly strong inflammatory response caused by their more powerful immune systems leads to more severe symptoms (6)

In addition to the strong inflammatory reaction during the first and third trimesters, pregnant mothers have other challenges to contend with. High levels of certain hormones can cause the upper part of the respiratory tract to swell (7), putting them at high risk of a respiratory tract infection (8). And the enlarged womb restricts lung expansion during the third trimester, causing a feeling of breathlessness (7)(8), again making pregnant mothers more susceptible to respiratory infections (7).

A flu vaccine is recommended for all pregnant women, whatever stage of pregnancy they’re at; the flu jab will help protect both you and your baby (1).




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