Being overweight when you're pregnant increases the chance of some complications such as gestational diabetes. If you are obese (usually defined as having a BMI of 30 or above) and pregnant, do not try to lose weight during your pregnancy. It will not reduce the chance of complications and may not be safe. The best way to protect you and your baby’s health is to go to all your antenatal appointments. This is so your midwife, doctor and any other health professionals can help with any problems you might face and take steps to prevent or manage them.
If your BMI is 30 or above, you are advised to take a higher dose of folic acid (5 mg per day).
The Royal College of Obstetricians and Gynaecologists (RCOG) information leaflet has all the current information to support you: https://www.rcog.org.uk/en/patients/patient-leaflets/being-overweight-pregnancy-after-birth/