Ideally your preconception weight should be within 7 kilograms of the ideal range for your height. If you are unsure what this is, you can check out your body mass index (BMI) using a BMI calculator. BMI is a measure of whether you're a healthy weight for your height.
If you are overweight you will need to adopt a healthy approach to eating and exercise to help you achieve a normal weight before you become pregnant.
Obesity can also lead to infertility, so if you have a serious weight problem see your doctor at least six months before trying to conceive and ask to be referred to a dietician. Alternatively, you could join a local gym.
Being significantly overweight or obese can cause complications when you become pregnant as you are more likely to develop diabetes or high blood pressure.
If you need to lose weight it is important to do this gradually by eating sensibly and taking regular exercise. Losing weight suddenly, or yo-yo dieting, can trigger stress mechanisms in the body and temporarily shut down fertility. Losing a lot of weight too quickly can also make the body go into starvation mode which temporarily leads to malnutrition, ultimately causing the body to shut down non-essential functions such as ovulating.
Therefore it is best not to go on any kind of slimming diet in the three months before trying for a baby unless on medical advice. With any kind of diet that restricts food intake there is a danger of missing out on key nutrients because such diets are not balanced.
Regular exercise, such as brisk walking or swimming, carried out for 20 minutes three times a week, will get you fit before conception and help your body cope better with the demands of pregnancy.
For more information and to use their BMI healthy weight calculator, visit NHS choices.