Metformin in Pregnancy

This leaflet is for women with:

• Gestational diabetes (diabetes diagnosed during pregnancy)
• Pre-existing diabetes that was diagnosed before pregnancy (usually Type 2 Diabetes) who are now pregnant or are planning pregnancy.

Why Metformin has been recommended

Metformin is offered to women for whom diet and exercise changes have not lowered glucose levels to the recommended targets as recommended by NICE (National Institute of Health and Care Excellence).

Is Metformin safe in pregnancy?

A large study published 2022 has shown no safety concerns relating to use in pregnancy. Metformin now has a license for use for Gestational Diabetes, for Type 2 Diabetes during pregnancy and when planning pregnancy

How Metformin works

• The exact mechanism is unclear but it can reduce the amount of glucose produced by the liver
• It allows the insulin produced by the body to work better to reduce blood glucose levels
• It works best when supported with the appropriate diet and exercise changes.
• It can be used with insulin.

Advantages of taking Metformin

• Improves diabetes control in preparation for pregnancy
• Lowers blood glucose levels in mother which then lowers amount reaching the baby and prevents too much weight gain in baby
• An alternative treatment of diabetes instead of insulin
• May lower the dose of insulin needed if insulin is required.

Working together with diet and exercise

It is important to continue with the dietary changes as advised by the dietitian as well as taking regular exercise (for example, walking for 30 minutes after a meal) while on metformin.

Side effects of metformin

Most people tolerate Metformin very well but some experience side effects which can be temporary. These include nausea, bloating, flatulence or diarrhoea.

Contact us if you suffer abdominal pains or vomiting. Try taking the tablets in the middle of a meal or straight after a meal with some water. Most side-effects usually settle after one to two weeks. If they do not settle, contact us for advice

Stop metformin if you have

Diarrhoea, vomiting, dehydration or any significant illness.

How to start metformin

Start with one 500mg tablet a day with your main meal. This can be increased every three to four days to a maximum of four tablets in total per day usually split into two doses. Your diabetes team can advise you on this.

After your baby is delivered

If you have gestational diabetes, Metformin can be stopped after delivery. You should refer yourself to the diabetes prevention programme: https://www.lwtcsupport.co.uk/gdm-info-page

If you have been on metformin for Type 2 diabetes before pregnancy, this can be continued, although your diabetes team will advise on individual cases.

Metformin can be taken while breast feeding.       

Contact numbers

We hope that you have found this information useful. If you have any questions or are worried about anything, please speak to the following Dorset County Hospital staff:

During working hours Monday to Fridays:

Diabetes Specialist Nurse – 01305 255342

Diabetes Specialist Dietitian – 01305 255526

Diabetes Department – Secretary – 01305 255737

About this leaflet

Author: Dr Mo-Lee Wong, Diabetes Consultant
Written: April 2026
Approved: April 2026
Review date: April 2029
Edition: v2

If you have feedback regarding the accuracy of the information contained in this leaflet, or if you would like a list of references used to develop this leaflet, please email patientinformation.leaflets@dchft.nhs.uk