Overweight and fertility when planning a pregnancy

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:

• thrombosis (blood clots)
• gestational diabetes (diabetes in pregnancy)
• high blood pressure
• pre-eclampsia.

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:

• miscarriage
• premature birth (where the baby is born before they are fully developed)
• stillbirth.

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:

• polycystic ovary syndrome (PCOS)
• underactive thyroid
• type 2 diabetes.

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.