• Being overweight or underweight can affect a woman’s fertility by causing hormonal imbalances and problems with ovulation.
  • In men, obesity can lower fertility.
  • Obesity in both women and men significantly increases the risks of infertility and pregnancy complications.
  • Compared with women in the healthy weight range, women who are carrying extra weight take longer to conceive.  
Please note: This page is about losing weight before getting pregnant. If you’re already pregnant and want to lose weight it’s important to talk to your GP or a dietitian first.

Most people know that being overweight or obese increases the risk of health problems such as heart disease and diabetes. But many are unaware that this also reduces fertility and the chance of having a healthy baby. If you are trying to get pregnant, or plan to start trying, the closer you are to a healthy weight, the greater your chance of conceiving (getting pregnant) and having a healthy baby.

Ideal weight for conception varies

The ideal weight for conception depends on how tall you are. Your body mass index (BMI) is a number based on your height and weight. The healthy BMI range is between 18.5 and 24.9. Adults with a BMI between 25 and 29 are considered overweight and a BMI over 30 indicates obesity. You can find out what your BMI is using our BMI tool.

Overweight and fertility

Being an unhealthy weight can affect a woman’s fertility by causing hormonal imbalances and problems with ovulation (releasing an egg from the ovaries). Obesity is also associated with polycystic ovary syndrome (PCOS), a common cause of low fertility or infertility. 

Being very overweight or obese can also reduce a man’s fertility. This is likely due to a combination of factors including hormone problems, problems with erection and other health conditions linked to obesity. 

For men, reaching a more healthy weight at least three months before conception can improve the chance of conception. This is because sperm take about three months to develop and being in the healthy weight range during this time helps develop healthy sperm. 

Overweight and pregnancy health

The environment in which eggs and sperm develop can affect the future baby’s health, and obesity can harm this environment. Getting closer to a healthy weight before conception increases the chance of the baby being healthy at birth and into adulthood.

Obesity and excess weight gain during pregnancy is also linked with a number of pregnancy complications. These include increased risk of miscarriage, high blood pressure, pre-eclampsia, gestational diabetes, infection, blood clotting, the need to induce labour, caesarean birth and stillbirth.

Babies born to very overweight mothers have an increased risk of childhood and adult obesity and other long-term health problems.

A small weight loss can improve fertility and pregnancy health

While the facts about obesity and reproductive outcomes can seem daunting, there is some good news. In women who are obese, even a small weight loss improves fertility and pregnancy health. Also, some dietary and lifestyle changes that limit weight gain during pregnancy can improve health outcomes for both mother and baby.

Getting ready for pregnancy

If you are planning to get pregnant, starting a healthy eating and exercise plan now improves your chances of getting pregnant and having a healthy baby. By making healthy changes to your diet and increasing your daily physical activity, you’ll be taking steps toward reaching a more healthy weight.

Tips for a healthier weight before pregnancy

Try these steps to a healthier weight:

  • Swap sugary drinks and alcohol for water.
  • Eat fast food less often and make healthier choices when you can. Make half your plate vegetables at lunch and dinner.
  • Use a smaller plate to help reduce your portion sizes.
  • Get moving every day. Fit in regular physical activity like walking to the shops, taking the stairs and walking with a friend.
  • Spend less time sitting by getting up regularly while using a computer or mobile device, and swapping screen time for other activities.
  • Choose healthy snacks like fruit, low-fat yoghurt or a small portion of plain nuts. Choose reduced-fat dairy and lean meat.
  • Set a realistic weight goal. It can help you feel motivated and active. Aiming for weight loss of half to one kilogram per week is a good goal.
  • Start a healthy eating and exercise plan together with your partner to increase the chance of getting pregnant and having a healthy baby.

Making these lifestyle changes will make a difference to your overall health, even if they don’t lead to weight loss. Begin making these changes before you start trying to conceive, and keep them up throughout your pregnancy and beyond.

Remember, if you’re already pregnant and want to lose weight it’s important to talk to your GP or a dietitian first, before you start making any lifestyle changes.

Underweight and fertility

Being underweight (BMI under 18.5) can reduce a woman’s fertility by causing hormone imbalances that affect ovulation and the chance of getting pregnant. Compared to women in the healthy weight range, underweight women are more likely to take more than a year to get pregnant. If you are underweight and trying to conceive, a dietitian can work with you to change your diet and help you put on weight.

Where to get help


More information

Reproductive system - female

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Fertility, pregnancy and childbirth

Content Partner

This page has been produced in consultation with and approved by: Victorian Assisted Reproductive Treatment Authority

Last updated: April 2018

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