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Healthy weight when trying to get pregnant

Considering your weight can be a part of planning to get pregnant.

Underweight, overweight or obesity can:

  • affect your chance of getting pregnant
  • increase your risk of pregnancy complications

If you are worried about your weight, your GP and other healthcare professionals can support you. But it's always a good idea to visit your GP for a health check before any pregnancy.

Body mass index (BMI)

BMI is a measure of your weight in relation to your height.

BMI alone does not give you a measure of your health. But a higher BMI can increase the risk of weight-related health conditions.

BMI does not measure muscle and fat. If you have a lot of muscle, you may have a high BMI despite having low body fat.

Calculating your BMI

To calculate your BMI:

  1. Measure your weight in kilograms.
  2. Measure your height in metres.
  3. Multiply your height in metres by itself. This is called your height squared.
  4. Divide your weight by your height squared.

Calculate your BMI - nhs.uk

BMI result

Your BMI result is a number in a BMI category. These categories do not diagnose weight-related health problems or obesity. They help to show if you may be at risk.

You may need to use different BMI categories depending on your ethnic background.

General BMI categories

General BMI categories for adults are:

  • underweight - 18.5 or less
  • healthy weight - 18.5 to 24.9
  • overweight - 25 to 29.9
  • obesity - 30 or more

Certain Asian, Black or Middle Eastern backgrounds

Use the following BMI categories if your background is:

  • South Asian
  • Chinese
  • other Asian
  • Black African
  • Middle Eastern
  • African-Caribbean

BMI categories for adults of Asian, Black or Middle Eastern backgrounds are:

  • underweight - 18.5 or less
  • healthy weight - 18.5 to 23
  • overweight - 23 to 27.5
  • obesity - 27.5 or more

Weight and getting pregnant

Underweight, overweight and obesity can affect ovulation. Ovulation is when your ovaries release an egg.

Oestrogen is a female sex hormone involved in ovulation.

If you have:

  • underweight, your body may make less oestrogen
  • overweight or obesity, your body may make more oestrogen

This can cause irregular ovulation and periods. It may also lower your chances of getting pregnant with fertility treatment.

How to improve your chances of getting pregnant

Foods to eat when planning a pregnancy

If you have underweight

You may have underweight if your BMI is 18.5 or less. There are many causes of underweight. Some of them you cannot control.

Your GP can:

  • help you understand why you may have underweight
  • check for a cause if you lose weight without trying or cannot gain weight
  • recommend ways to manage your weight

They may refer you to another healthcare professional. This depends on the cause.

If you are trying to gain weight, it's important to do it gradually and eat healthy foods.

How to eat well

If you have excess weight

If your BMI is 30 or more, you may have a higher risk of obesity.

There are many causes of excess weight. Some of these also affect fertility, for example, polycystic ovary syndrome (PCOS).

If you are trying to lose weight, it's important to:

Your GP can:

  • check if you have any health conditions linked to your weight
  • recommend ways to manage your weight
  • tell you about support available in your area

They may refer you to another healthcare professional depending on your needs.

Slaintecare logo
This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 21 May 2026
Next review due: 21 May 2029