Overweight and fertility when planning a pregnancy

Being a healthy weight helps with fertility, pregnancy and the future health of the child.

Note: This page is for you if you have a high BMI (if you are overweight). If you have a low BMI (underweight), there is information here for you.

Can being overweight (having a high BMI) affect my fertility?

Being overweight or obese may affect your fertility. This means that it may make it harder to get pregnant. Bringing your BMI down before you get pregnant, even by one or two points, will help reduce your risk of complications. 

Most women and birthing people who are overweight have a straightforward pregnancy and birth and have healthy babies. But being overweight or obese during pregnancy can cause health problems during pregnancy and affect your child’s future health.

Having a high BMI and getting pregnant

BMI stands for Body Mass Index. It is used to work out if your weight is in a healthy range.  

BMI is not a perfect way to measure your weight because it can’t tell the difference between fat, muscle or bone. But it is still the best way of assessing your weight.

The ideal BMI for getting pregnant is between 18.5 and 24.9. This is known as the healthy range.  

If you have a high BMI, bringing it closer to the healthy range before trying for a baby will help you get pregnant and reduce the risk of pregnancy complications.

Many people do not lose weight easily and it can sometimes feel like an impossible task. But try not to lose heart. Losing a small amount (5-10%) of your weight would have significant health benefits and increase your chances of getting pregnant.

BMI weight ranges

The BMI weight healthy range is different for different ethnicities.  

People with a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background have a higher risk of developing some long-term conditions, such as type 2 diabetes, with a lower BMI.  

If you are in these groups a BMI:

  • below 18.5 is underweight
  • between 18.5 and 23 is healthy  
  • over 23  means increased risk (overweight)
  • over 27.5 means high risk (obese).

For people of White heritage, a BMI:

  • below 18.5 is underweight
  • between 18.5 and 24.9 is healthy
  • between 25 and 29.9 is overweight
  • of 30 or over is obese.

Why does the BMI calculation change for different ethnic groups? 

The BMI definition of obesity (a BMI of 30+) was originally developed using data mostly from White populations. Since then, research has found that people from a South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background, have a higher risk of developing some long-term conditions, such as type 2 diabetes, when they have a lower BMI.

As a result, the NHS has developed guidelines to make sure that people from these ethnic backgrounds get help to prevent developing type 2 diabetes earlier than people from White backgrounds.

There is not enough evidence yet to say whether people from different ethnic backgrounds should have different pregnancy care based on their weight.

This means that the advice and care you will have about your weight in pregnancy is the same for all women and birthing people, whatever your ethnic background. 

BMI Calculator

BMI calculator

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Men, fertility and weight 

Men can improve their chances of getting their partner pregnant by making sure their BMI is in the healthy range. Maintaining a healthy weight is essential for keeping sperm in good condition. Find out more about how to improve male fertility.  

Having a high BMI during pregnancy

Most women and birthing people with a high BMI have a straightforward pregnancy and have healthy babies. But having a high BMI (a BMI over 25) increases your risk of pregnancy complications such as:

You’re also more likely to be offered an induction or caesarean section.

High BMI and risks to baby

Having a high BMI can also increase the risk of:

The higher your BMI, the greater the risk. Bringing your BMI down before you get pregnant, even by one or two points, will help reduce your risk of complications. 

Dieting during pregnancy is not recommended because you might cut out nutrients that your baby needs. That’s why it is important to try and lose any excess weight before you get pregnant.  

Try not to get overly worried if you are overweight when you get pregnant. Your midwife or doctor will monitor you and your baby closely.

There are also lots of things you can do to stay well in pregnancy, such as staying active and eating a healthy, balanced diet.  

If your BMI is over 30 when you get pregnant you may have more antenatal appointments (visits to the midwife) during your pregnancy because of the higher risk of problems. You may also be advised against some birth choices, such as a home birth.

Reasons for being overweight 

The reasons why people become overweight or obese are complex. It may be caused by:

  • eating food high in calories, such as processed or fast food
  • drinking too much alcohol
  • eating large portions
  • not doing enough exercise
  • genetics – there are some genes associated with being overweight
  • not having access to healthy food.

Medical reasons for weight gain

There are also some medical conditions that may cause weight gain and make it harder to lose weight. Some of these conditions can cause fertility problems (difficulties getting pregnant) or problems during pregnancy.  

These include:

See your GP if you think you may have a health issue that is causing weight gain or may be making it harder for you to lose weight.

Emotional overeating 

Some people use food as a way of coping with their emotions. Your GP can also help if you need support from a trained healthcare professional, such as a therapist, to change the way you think about food and eating.

UK Charity Beat has more information about emotional overeating.

It's important to look after your mental wellbeing if you are trying to get pregnant. There is support available if you need it. Find out more about looking after your mental wellbeing while trying to get pregnant.

Tips for losing weight

  • Eat a healthy, balanced, calorie-controlled diet  
  • Be physically active, doing activities, doing activities such as fast walking, jogging, or swimming for 150 to 300 minutes a week (for example 30 minutes a day)(2.5 to 5 hours a week)
  • Eat slowly and be aware during times where you could be tempted to overeat, such as eating out or all-you-can-eat buffets
  • Avoid sitting for long periods of time – this is bad for you before, during and after pregnancy
  • Try the NHS Couch to 5k or the Active 10 app, which has helped thousands of people with a high BMI to become active.
  • When you are shopping use the NHS food scanner app, which shows quickly and easily how much sugar, sat fat and salt is inside your food and drink. 
  • Set yourself realistic goals such as, ‘I will bring my BMI down by 2 points’. This will give you something to work towards.  
  • Think of something that you can do when you have  a food craving – such as drinking a glass of water – this gives you a feeling of fullness, which may help.

Mental health medication and weight

Some medicines, including those that treat schizophrenia, bipolar disorder and severe depression (antipsychotics) can cause weight gain. This is because they can make you feel hungry, so you eat more. They can also make you feel tired, so you’re less likely to be active. If you’re taking these medicines, it’s even more important to follow a healthy diet, and keep active, to help prevent or reduce weight gain.

If your weight gain is caused by your mental illness medication, talk to your doctor and see whether they would be willing to prescribe something else instead. It’s vital not to stop taking your medication without speaking to your doctor first.

Read more about serious mental illness and planning a pregnancy here.

Do not try crash diets or over exercise

Following crash diets, skipping meals or suddenly doing lots of exercise over a short period of time is unlikely to help with losing weight. Successful weight loss involves making small changes that you can stick to for a long time.

A good diet programme will:

  • help you learn about healthy eating, and portion sizes
  • not be too restrictive about what you can eat
  • be based on helping you reduce your weight gradually, rather than short-term, quick weight loss, which is unlikely to last.

Your GP can tell you about local weight loss groups available. These could be provided by the local authority, the NHS or a private company service, which you will need to pay for. You can also find details of weight loss support groups on the NHS website.

Speak to your GP can if you need more advice you about lifestyle changes and how to improve your diet. They may also be able to referrer you to a dietitian.  

Clinical Knowledge summaries (2023) Pre-conception – advice and management. https://cks.nice.org.uk/topics/pre-conception-advice-management/

Royal College of Obstetricians and Gynaecologists (2022) Being overweight in pregnancy and after birth patient information. https://www.rcog.org.uk/for-the-public/browse-all-patient-information-leaflets/being-overweight-in-pregnancy-and-after-birth-patient-information-leaflet/

NICE Guidelines (2010) Weight management before, during and after pregnancy. National Institute for Health and Care Excellence https://www.nice.org.uk/guidance/ph27

NHS. What is the body mass index? https://www.nhs.uk/common-health-questions/lifestyle/what-is-the-body-mass-index-bmi/ (Page last reviewed: 28 November 2022 Next review: 28 November 2025)

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Rishi Caleyachetty, PHD et al (2021) Ethnicity-specific BMI cut offs for obesity based on type 2 diabetes risk in England: a population-based cohort study. The Lancet Diabetes & Endocrinology

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Holt RIG. (2019) The Management of Obesity in People with Severe Mental Illness: An Unresolved Conundrum. Psychother Psychosom. 88: 327-332. https://karger.com/pps/article/88/6/327/283157/The-Management-of-Obesity-in-People-with-Severe

Firth J et al. (2019) The Lancet Psychiatry Commission: a blueprint for protecting physical health in people with mental illness. Lancet Psychiatry 6: 675–712.

Review dates
Reviewed: 29 August 2023
Next review: 29 August 2026