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Immune system
Pregnancy Mar 18, 2020
7 Minutes

The immune system and pregnancy: stronger than you may think…

The old way of thinking was that when a fertilised egg (which has DNA which is 50% not your own) implants, it is a result of ‘suppression’ of the immune system. Without this, the body would see ‘foreign cells’ and reject it. Sort of like what happens when you have an organ transplant. Therefore pregnancy requires constant suppression of the immune system to ensure the body doesn’t reject cells that are not its own. Well, it seems when it comes to pregnancy: this analogy is not actually correct. In fact, recent research shows that far from a consistently suppressed immune system, a ‘dynamic and adaptive immune system’ is required for a successful pregnancy.

So, no, it is not ‘suppressed’ it is just a bit different. Here is what you need to know. 

What actually happens to your immune system when you’re pregnant? 

The immune system does change. It is not the same as pre pregnancy. That is for sure. However, it is not as simple as it is constantly ‘suppressed’ through pregnancy. In fact, research has shown that it changes with the stages of pregnancy and depending on the levels of pregnancy hormones.

Pretty clever stuff!

‘It is appropriate to refer to pregnancy as a unique immune condition that is modulated, but not suppressed’ (1, 5)

One paper argued that pregnancy represents the most important period for the conservation of the species and therefore it is fundamental to strengthen all the means to protect the mother and the offspring. (1)

So, it makes sense that the immune system gets even more ‘dynamic’ at this stage. Which appears to be the case.

Different responses and for different stages….

It appears that the body and immune system are actually very clever, dynamic and active during pregnancy. Responding to the needs of the developing foetus, the stage of development and hormonal shifts. In fact, hormone receptors are found on most immune cells. (7).

The downside to this very clever process is that it can make predicting how a pregnant body will react to a microorganism a bit tricky. There are still lots we do not know. Particularly when we have new bacteria or viruses on the scene.

The good news: you actually need a very robust immune system to enable implantation… 

Several papers have actually shown that rather than being suppressed to allow for implantation. The immune system is in fact ‘active, functional and is carefully controlled’ (1)

Implantation requires a strong immune response. As a fertilised egg implants through the epithelial lining, research has likened the immune state to that of an ‘open wound’. One that requires a ‘strong inflammatory response’ (1, 5) in order to repair the uterine lining and remove cell debris.

More of an ‘active’ process helping the body tolerate the foetus rather than one of suppression…

Next up: a shift into the second trimester – the immune system makes you feel better! 

It is thought (along with hormonal fluctuations) that the above can contribute to feeling unwell and run down during the first trimester. The immune system switch that comes around 13 weeks (5) can similarly help reverse this and make the mother feel better (1).

At this point the immune system switches to an anti-inflammatory state. (1,5) As the foetus switches into growth mode.

Finally the immune system switches again for birth: 

As the body prepares for birth the immune system switches gears again back to a pro inflammatory state. Necessary for labor. In fact, we see an influx of immune cells into an area of the uterus which plays a big role in contractions: the myometrium. (5)

Once again, all pretty necessary stuff.

A changed but very robust, adaptive immune system… 

During a normal pregnancy, the lining of the uterus contains a high number of immune cells such as macrophages, natural killer cells and regulatory T Cells. On the flip side, there are a reduced number of B cells and T Lymphocytes. So, it is not quite the same as before, but it plays a key role in keeping the pregnancy and trying to keep mother and baby healthy at the same time. A delicate balance.

The placenta as a defender… 

The outer layer of the fertilised egg which will become part of the Placenta is known as a Trophoblast. It has been shown to produce Antimicrobial peptides for defence. Playing a role in helping protect a baby from transmission of an infection from the mother. HIV being an example. (1)

Not only do crucial cells in the placenta (Trophoblasts) produce antimicrobial peptides, they have also been shown to produce important anti viral factors (1).

‘Most viral infections affecting the mother do not [transmit] to the foetus, suggesting that the placenta may play an important role as a potent immune-regulating interface protecting the foetus.’ (1)

It also seems that although infections are common during pregnancy, passage through the placenta and an infection for the baby appear to be the exception rather than the rule. (1)

However, an unborn baby can cause a different immune reaction from the mother than pre pregnancy: 

Although the immune system is not suppressed, the changes can cause an altered response to invaders than you may see from someone who is not pregnant. For example, the H1N1 influenza outbreak (Swine Flu) in 2009 did cause a different and more severe reaction in many pregnant women which is why the flu vaccination is strongly recommended for pregnant women. (7)

It appeared to make clearing the virus from the lungs more challenging as well as causing significant inflammation as a response to the virus through the body.

The good news is that this is another virus that did not appear to cross the placental barrier and infect the unborn baby. However, severe immune/inflammatory response in the body of the mother did in some cases lead to complications such as preterm birth. (7).

Recurrent miscarriage: When our immune systems go wrong?

There is emerging research which suggests that recurrent miscarriage could be linked to our immune systems failing. Specifically when naturally occurring ‘killer cells’ get more aggressive. Check out the need to know on this from specialist Dr Hassan Shehata. His focus is on restoring balance to the body’s immune system to allow a successful pregnancy. Fascinating stuff.

So what’s the conclusion to all of this? 

Well. Firstly, do not believe that your immune system is ‘suppressed’ if you’re pregnant. It is however changed and changing. It is managing the very delicate balance of protecting you/your baby and allowing ‘foreign’ cells to grow. Clever stuff.

The reality is however, a pregnant body and immune system can react differently to infection than a non pregnant body. There are still a lot of unanswered questions and things we don’t understand. So, it is always important to make sure you’re up to date with your vaccinations and of course to practise good health, hygiene and make sure you’re supporting your immune system and it’s home: the gut.

The gut microbiome is home to up to 70% of the immune system: 

Analysis of the immune system’s role in implantation and growth of a baby during pregnancy shows once again evidence that the gut microbiome matters. This has been shown in animal studies. Click here to read more. 

The great news here is that research has shown this can be changed in as little as 24hrs by what you eat. Click here for more. 

It’s not rocket science either: lots of whole, unprocessed fruits and vegetables. Diversity is good. Plus lots of fibre (prebiotic food) which can feed the good bacteria we already have.

For a science backed: ‘how to’ boost during pregnancy click here. 

Vitamin D: it’s back again! 

Most of us associate Vitamin C with good immune health. As an antioxidant it is certainly useful in helping reduce damage from infection (although the jury is still out as to whether or not it does anything other than potentially reduce severity and duration of infection).

Vitamin D is very interesting when it comes to immunity. There is now a compelling body of research that backs up it’s support of a healthy immune system for everyone. Click here for more. 

However, for the pregnant immune system: it appears to play a role in the development and function of the placenta and by exerting ‘immunomodulatory effects critical for pregnancy maintenance’ (2).

So: make sure you’re getting enough. Click here for more. 

Self care and the immune system: 

Finally – relax and look after yourself. Taking a bit of extra care of your mental health will not only make you feel better but will also support your body and immune system. Research has shown how powerful things like mindfulness and meditation can really be. Click here for more. 

Click here for ten tips to manage anxiety from our resident guru on all things mind health: Emmy Brunner: 

Then how easy a bit of self care can really be from author of several books on the subject and psychologist Suzy Reading. Making it easy here! 


1) Mor G, Cardenas I: The Immune System in Pregnancy: A Unique Complexity: America’s journal of reproductive immunology. 2010 Jun: 63(6):425-433

2) Cyprian F, Lefkou E, Giradi G: Immunomodulatory Effects of Vitamin D in  Pregnancy and Beyond: Frontiers of Immunology: 2019: 10


4) Gaudilliere D, Ganio G, Aghaeepour N: An immune clock of human Pregnancy: Science Immunology: 2017

5) Mor G, Aldo P, Alvero A: The unique Immunological and microbial aspects of pregnancy: Nature Reviews Immunology: June 2017

6) Meijer M, Van Noortwijk A: Influenza virus infection in pregnancy: a review: ACTA Obstericia et Gynecologica Scandinavia

7) Littauer E, Stein E: H1N1 influenza virus infection results in adverse pregnancy outcomes by disrupting tissue-specific hormonal regulation: PLoS Pathogens: 2017 Nov: 13(11)


This article is for informational purposes only. This article is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. The information on this website has been developed following years of personal research and from referenced and sourced medical research. Before making any changes we strongly recommend you consult a healthcare professional before you begin.

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