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This page explains what Gestational Diabetes Mellitus (GDM) means, how it may affect you and your baby, and how your pregnancy will be managed to help you have a healthy pregnancy.
If you have any questions, please ask your healthcare team.
GDM is a type of diabetes that happens only during pregnancy.
- It is usually temporary and most women (about 90%) recover after the baby is born.
- It happens because your body cannot use insulin properly or make enough insulin during pregnancy.
You will be offered a diabetes test if you have certain risk factors, such as:
- BMI over 30
- previous baby weighing 4.5 kg (10 lbs) or more
- had GDM before
- family history of diabetes (in close relatives; your parents or siblings)
- certain ethnic backgrounds
- signs during pregnancy like extra fluid, large baby, or sugar in urine
- some medicines that increase risk
If blood sugar is not controlled, it can cause:
- macrosomia – baby grows larger than normal because extra sugar turns into fat.
- polyhydramnios – more fluid than normal around baby, which can cause your waters to break early, early labour or heavy bleeding after birth.
- jaundice – your baby’s skin, eyes or mouth look yellow; sometimes needs light treatment in hospital.
- breathing problems – your baby may breathe fast or grunt at birth; usually gets better in 24 hours.
- low blood sugar after birth – known as hypoglycaemia. Feeding your baby as early as possible will keep sugar levels normal. Breastfeeding helps. Harvesting your colostrum from 36 weeks of pregnancy is a good idea.
Your baby will not have diabetes when born.
Other Risks
There is a small risk of:
- Preterm labour
- Growth problems
- Stillbirth (very rare)
If you have GDM, your pregnancy will be considered high risk. Good blood sugar control reduces these risks.
You will be cared for by:
- obstetricians
- diabetes specialist midwives
- possibly a diabetologist, diabetes nurse, and dietitian
You will have visits every 1–4 weeks and phone support in between.
The main goal is to keep blood sugar close to normal by:
- eating a healthy diet
- doing gentle exercise
- checking blood sugar regularly
- taking medicine (metformin or insulin) if needed
- You will prick your finger 4 times a day using a lancing device and test on a glucose meter.
- Test before breakfast and 1 hour after each meal.
- Record results in a diary or app.
Targets:
- before breakfast: below 5.3 mmol/L
- 1 hour after meals: below 7.8 mmol/L
If you have 3 readings above target in a week, call your diabetes midwife or nurse.
Checking your blood sugar and writing down the results is very important.
These results help your diabetes team decide the best care for you.
Please make sure you:
- test at the right times
- record your results clearly
If you have any problems, ask for help. We are here to support you.
If you are cared for at Wexham Park Hospital, you will be offered a live online group session with a diabetes specialist dietitian. After the session, you can ask for telephone consultations if you need more help.
Regular exercise helps control blood sugar, manage weight, and keep you healthy during pregnancy.
If your pregnancy is uncomplicated, you can do activities like:
- brisk walking
- swimming
Aim for 30 minutes every day. Always talk to your doctor or midwife before starting any exercise program.
If healthy eating and exercise do not keep your blood sugar under control, you may need medication.
Metformin is a tablet that:
- helps your body use insulin better
- improves insulin resistance
- does not cause low blood sugar
It starts at a small dose and is increased slowly.
Side effects can include bloating, nausea, or wind.
If this happens, tell your diabetes team.
If metformin does not work or you cannot take it, you may need insulin injections.
- Insulin is given using a simple pen device.
- It helps lower blood sugar and supports your baby’s growth.
If you take insulin for more than 3 months, you must inform the DVSA if you drive, because insulin can sometimes cause low blood sugar.
To make sure your pregnancy is going well and your baby is healthy, you will have some extra tests:
- HbA1c blood test. This shows your average blood sugar over the last 3 months.
- ultrasound scans. From 28 weeks, you will have a scan every month to check:
- your baby’s growth
- the amount of fluid around your baby
If there are any concerns, scans may be done every 2 weeks.
We recommend a hospital birth on the labour ward so you and your baby can be carefully monitored.
This helps prevent and manage any complications after birth. Some women with GDM may be able to give birth in the birth centre, your obstetrician will tell you if this is safe for you.
- If you only needed diet changes (no insulin), your pregnancy can continue normally. You will be offered induction before 41 weeks.
- If you are on insulin, induction is usually offered at 37–39 weeks. The exact timing depends on:
- your blood sugar levels
- insulin needs
- your baby’s growth
This will be discussed with you at your clinic visits.
When you come into hospital, please bring:
- your blood glucose testing machine
- test strips and lancets
- any medication you are taking
- your hypo treatment (if you use one)
Checking Your Baby
- Your baby’s blood sugar will be checked within 4–6 hours after birth, and at least a couple of times more.
- This is a simple blood test.
- You and your baby will stay in hospital for at least 24 hours.
Your Medication
- If you were taking insulin or metformin, this will stop after birth.
- You will check your own blood sugar for the first 24 hours:
- before meals: below 7 mmol/L
- 1 hour after meals: 6–10 mmol/L
Yes! Early breastfeeding is encouraged because it helps keep your baby’s blood sugar normal.
Breastfeeding is the best food for your baby and passes your immunity to them.
Colostrum Harvesting
- Colostrum is your first breast milk and is perfect for your baby’s immune system.
- You can start expressing colostrum from 36 weeks and freeze it for after birth.
- This is especially helpful if you have gestational diabetes, twins, planned caesarean, or other special circumstances.
- Ask your midwife for advice and read our page about colostrum harvesting.
Gestational diabetes can feel overwhelming.
- Some women feel anxious about complications or changes to their birth plan.
- Remember: most women with GDM have healthy pregnancies and babies when blood sugar is managed.
- You will have extra care and support from your specialist team.
If you feel stressed or worried:
- Talk to someone close to you (partner, friend, family).
- Speak to your diabetes team, they can refer you to NHS Talking Therapies, or you can self-refer.
- You will need a fasting blood sugar test at your GP surgery 6–13 weeks after birth.
- About 35–50% of women with GDM develop Type 2 diabetes within 5 years.
- To reduce risk: k
- keep eating healthily
- maintain a healthy weight
- exercise regularly
Future pregnancies:
- There is a 50% chance GDM will return.
- You will have an early glucose test and another at 24–28 weeks.
Your GP needs to know you had GDM.
They will arrange annual blood sugar tests to check for early signs of diabetes.
Questions
No question is too small—please ask if you are worried.
By working together with you on diet, exercise, and blood sugar checks, we can make this pregnancy safe and positive for you and your family.
Contact us
If you have any queries relating to this information, please contact the Maternity service.
About this information
Service:
Maternity
Reference:
M/024
Approval date:
1 March 2026
Review date:
1 March 2029
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Important note
This page provides general information only. It is developed by clinical staff and is reviewed regularly every 3 years for accuracy. For personal advice about your health, or if you have any concerns, please speak to your doctor.