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Weight gain pregnancy
Pregnancy Sep 21, 2020
6 Minutes

Another evidence-based way to reduce risk of allergy: pregnancy weight gain

Weight gain is a very tricky subject at any time in one’s life. During pregnancy it feels even more charged. Major hormone changes, sickness, fatigue and emotional ups and downs all contribute to the challenge. It’s tough! There is also the fact that your body is changing dramatically before your eyes which adds a very real mental health component. Many of us will (particularly during the first trimester) reach for comfort foods that we would ordinarily avoid. That is of course totally normal. However, it is also important that we do what we can to stay within the ranges of ‘healthy weight gain’ during pregnancy. The latest research says making an effort to do this could in fact be a real positive – specifically by reduce your child’s risk of developing something that is rampantly on the rise in kids these days: allergies. Here’s what you need to know: 

How much the evidence says we ‘should’ be aiming for when it comes to healthy pregnancy weight gain: 

First and foremost, pregnancy is not a time for dieting. Nor, however is it a time for rampant indulgence. We now know that the old mantra of ‘eating for two’ is complete nonsense. However, it can be hard to know what the ‘ideal’ amount aim to gain is. As always there is a lot of noise and conflicting information.

Not quite a one size fits all when it comes to healthy gains: 

The reality is different people have different builds and situations. Which is why putting an exact number or even range can be tricky. Not to mention the difference between singleton/twin/multiple pregnancies and pre pregnancy BMI. By far and away the most sensible thing to do (if you’re concerned) is to bring this up with your doctor. Particularly if you have a genetic history of things like allergies, diabetes or other health issues. Your doctor will work with you to keep you within the range that is right for you as an individual. Sometimes you just need to speak up. Doctors can be busy people. However, this article will explain why it is important to speak up and to be conscious of this. Specifically because the latest research suggests that a healthy weight gain can actually reduce the odds of your child developing a major allergy. 

There are some official guidelines when it comes to ‘ideal’ pregnancy weight gain: 

The Institute of Medicine in the US (IOM) released guidelines back in 2011 suggesting that for women with a normal starting BMI (between 18-25) the ideal is to remain with a total gain of between 22-33lbs (that’s around 11.5-16kg). 

For twins (for those with a normal BMI) the weight gain range is recommended: 16.8-24.5kg. 

Once again, these are suggested ranges. However, many women are gaining more than this during pregnancy. Not only has this been linked to development of allergies. It has also been linked to many issues for birth and post. In fact, research showed that nearly 50% of pregnant women now exceed these levels. 

So, where do we gain most of the weight during pregnancy? 

Weight gain is of course essential when we are growing an entirely new human. Many things are changing. From the way our bodies take energy from food (which can give rise to gestational diabetes when it goes wrong – click here for more) to a big increase in blood volume, to finally ending up with an entirely new person inside of us. 

The main factors that are behind pregnancy weight gain however are:

  • change in body composition (balance between fat/muscle depending on activity, hormone and metabolic changes during pregnancy)
  • Weight of the baby
  • Weight of the placenta
  • Amniotic fluid
  • Extra blood and water volume within the body 

The myth of ‘eating for two’: how much more we really need: 

Cravings and feeling unwell particularly in the first trimester will likely see our attitude to food change. That’s ok. Sometimes you have to do what you have to do! There are limits however for those seeking a healthy pregnancy. Luckily by now most of us appreciate that the old mantra of ‘eating for two’ is a complete misnomer. In fact: 

The UK’s National Institute for Health and Clinical Excellence (NICE) advises that only 200 extra calories per day are required if one is a normal BMI. That is only in the last trimester. With 30 minutes per day of physical activity. So, as you can see. Most certainly not eating for two…. 

How does excess weight gain during pregnancy link to allergy development? 

There have been many studies drawing links between higher BMIs pre pregnancy and increased risk of allergy in children. We also know that there are many factors behind why a child can develop an allergy (genetics is one element but there are likely environmental in addition). Click here for a deep dive with top paediatric allergist Professor Gideon Lack. However, the latest body of research (1) focusing on nearly 16,000 mother/child pairs over eight years adds to the importance of staying within an appropriate level of gain during pregnancy. 

Here are the stats: 

The study showed that women who gained between 33-55lbs had a 13% higher risk of a child with asthma, allergic rhinitis, food allergy. 9% increased chance of eczema. 

For those who gained more (+55lbs) the risk of developing asthma rose to 22%, food allergy 20% and eczema to 15%. 

The risks were also far higher if the BMI was above normal range (+25) pre pregnancy. 

So, how does excess weight gain during pregnancy contribute to allergy development?

As above. The one thing we do know for sure when it comes to developing allergies is that there are likely many factors at play. However, we do know that when a mother has excess weight gain there are several knock on effects which could increase the risks: the principal one being inappropriate inflammation. Click here to read a lot more about why this is on the rise and why it is an issue. However, in a nutshell: we know inflammation can be caused by (and causes) inappropriate immune response. We also know it happens when there is excess fatty (adipose) tissue. This can have several knock on effects. According to the research (1) we know that:

The research also showed that keeping below the maximum guideline when it comes to weight gain meant a lower risk of childhood allergies: 

This was the case when it came to women who were within the range of normal BMI pre pregnancy. 

Bottom line? 

Weight gain around pregnancy is a hard subject. It’s not always easy to get a handle on and many of us feel uncomfortable as it is with our changing bodies – as much as we want the end result! However, as always we believe knowledge is power and here is yet more evidence that maintaining (where we can) a healthy lifestyle an activity level during pregnancy is ideal when it comes to increasing the odds of a healthy baby. There is nothing wrong with indulging our cravings now and again (and hard to fight, especially in the first trimester!) however ensuring that it is in moderation can go a long way to a healthy outcome. 

Click here for more on exercise during pregnancy from our resident pre and post natal specialist trainer Natalie Ferris.

We also know and appreciate what an emotional time it is. Click here for more on body image during pregnancy and how this is often a real struggle for our mental health.

Finally, once again everyone is unique and if you are concerned or confused as always the first port of call is to speak to your doctor. Be your/your baby’s best advocate! 


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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