Gestational Diabetes Mellitus (GDM)

Patient Experience

  • Reference Number: HEY-816/2023
  • Departments: Maternity Services
  • Last Updated: 3 April 2023


This leaflet has been produced to give you general information about your condition. If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team.

What is Gestational Diabetes Mellitus (GDM)?

Gestational Diabetes Mellitus (GDM) is a condition which develops during pregnancy and leads to high levels of glucose in the blood. Insulin is a hormone that is produced by the body to lower blood glucose levels. In pregnancy, hormonal and other changes mean that insulin is not able to work as well in the body, so the body needs to produce more insulin. In some women, the body is unable to produce enough insulin, and blood glucose levels will rise.

What are the risk factors for developing GDM?

  • Gestational diabetes in previous pregnancies.
  • Previous large baby over 4.5kg.
  • Body mass index (BMI) over 30kg/m².
  • Family history of diabetes.
  • Minority ethnic family origin with a high prevalence of diabetes.
    • Previous stillbirth
    • PCOS
    • Twins

How is GDM diagnosed?

If you have any of the above risk factors, you will be checked for GDM at your booking appointment with the midwife, and again at 28 weeks pregnancy. GDM will be diagnosed if you have a HbA1c level ≥41mmol/l at booking, or ≥39mmol/l at 28 weeks. Or if your have a Random Plasma Glucose of ≥9 mmol/l.

What are the risks of GDM?

GDM can carry serious risks to you and your baby if not diagnosed and treated.

Risks include:

  • The baby may grow too big in the womb. This can make it difficult to give birth vaginally and you may need a Caesarean section.
  • Stillbirth
  • Raised blood pressure during the pregnancy (pre-eclampsia)
  • Preterm (early) labour

You will be regularly monitored to check the growth of the baby to reduce these risks. You may need a discussion with your healthcare team about the safest way to deliver your baby.

What steps can I take to reduce the risks?

Blood glucose (BG) monitoring

Regular blood glucose (BG) monitoring can help you keep track of your progress, and your healthcare team to identify any problems at an early stage.

You will be given a diary to record your values. These will be reviewed by your healthcare team weekly.

Test strips and lancets will be on prescription from your GP together with a special yellow sharps bin for disposing of the used lancet needles. The sharps bins must be disposed of by the local council. Telephone (01482) 300300 for Hull, or (01482) 393939 for East Riding.

Dietary changes

Glucose in the blood comes from carbohydrates in the diet. Carbohydrates are the foods that contain sugars and starches. All carbohydrates are digested into glucose that is absorbed into the blood and used to provide the body with energy. To prevent blood glucose becoming too high, we can reduce the carbohydrate we eat. Carbohydrate-containing foods are listed below:

How much carbohydrate should I be eating?

Fruit and vegetables

Aim for 5 portions per day. A portion is around a handful or 80g.

Vegetables and salad will not affect your glucose levels so can be eaten freely. They are also a good source of fibre, vitamins and minerals.

Fruits should be limited as they contain carbohydrate. Only have one portion at a time and up to 2 portions/day. Avoid fruit smoothies and fruit juices as these can be very high in sugar.

Milk and other dairy products

Milk does contain carbohydrate, but relatively small amounts. Milk is also an excellent source of protein and minerals, including calcium, essential for your baby’s development.

Aim for 3 portions of dairy per day eg 1 small glass milk (200ml), 1 pot diet yoghurt (150g), 30g any cheese.

Unsweetened nut and coconut milks are suitable alternatives to dairy products.



Fruit juices and smoothies can be very high in sugars, so are best avoided.

Carbonated sugary drinks including Coca-cola, Pepsi, Lucozade, Sports drinks are high in sugar and should be avoided. Sugar-free/diet /zero versions have artificial sweeteners eg. aspartame or saccharin and are safe to take in small amounts.

Diabetic foods T

These are not recommended as they can have a laxative effect.

How many carbohydrates should I be aiming for?

Aim to eat 3 meals and up to 2 snacks per day.

Menu ideas:

Breakfast 20-30g carbohydrate – examples include one of the following:

  • 2 small slices of toast with spread
  • 4 tablespoons cereal such as cornflakes / bran flakes / rice cereal with milk
  • 2 wheat biscuits with milk
  • 2 x poached or scrambled eggs on 1 x toast
  • small pot yoghurt with 1 piece of fruit
  • 30g porridge oats made with milk 

Lunch 40-50g carbohydrate – examples include one of the following:

  • 2 medium sliced bread sandwich with protein filling such as meat / cheese / egg / fish with piece of fruit
  • small tin of baked beans on 1 slice toast and piece of fruit
  • small jacket potato (weighing 200g when cooked) with salad and cottage cheese / cheese

Evening meal 40-50g carbohydrate – examples include one of the following:

  • 4 tablespoons pasta with meat / fish and salad / vegetables
  • 4 tablespoons basmati rice with meat / fish and salad / vegetables
  • 4 egg size potatoes with meat / fish and salad / vegetable
  • small jacket potato (weighing 200g when cooked) with meat / fish and salad / vegetables

Follow with a small pot of diet yoghurt or piece of fruit, small scoop ice cream (weighing approx. 40g).

Try and avoid sauces as they can contain carbohydrate eg sweet and sour, béchamel sauces and gravies.

Snack Ideas (10-15g carbohydrate)

  • Small piece of fruit eg apple / pear / banana
  • 2 crispbreads and low fat cheese
  • Small pot diet / light yoghurt
  • 2 x rich tea, malted milk or plain biscuits


Carbohydrate-free snacks can be eaten at any time:

  • Raw vegetables / salad with humous / salsa dip / cottage cheese
  • Handful nuts / mixed seeds
  • Olives / sundried tomatoes
  • Sugar free jelly
  • Beef/fish jerky

 What types of carbohydrates should I eat?

Remember – carbohydrates are essential to provide your body with energy. You should include carbohydrate at each meal. However, by swapping high sugar, processed and refined carbohydrates for starchy, high fibre and unprocessed carbohydrates, you will help to prevent rapid rises and falls in blood glucose. In addition, unprocessed carbohydrates have lots more fibre, vitamins and minerals and can also help keep you fuller for longer.

What else can I do? Keep active!

Activity increases the amount of glucose used by your muscles for energy, so it helps to lower your blood glucose levels. Also, being active helps the body use insulin more efficiently.

There are lots of other health benefits – being active can help with weight loss, lowering blood pressure, reducing stress and helping sleep. It can also reduce your risk of diabetes later in life.

What should I aim for?

  • Regular activity, such as 30 minutes of walking after lunch or dinner, to improve blood glucose levels.
  • Try and include muscle strengthening exercise about twice a week eg. Stretches, yoga or swimming
  • Try to avoid sitting for long periods of time, and try to build exercise into your daily life, such as taking the stairs instead of the lift.


My Blood glucose are still above target. Medications are the next step

Metformin (tablet)

This helps your own insulin to work more effectively, thus reducing some of the insulin resistance associated with pregnancy hormones. It is considered safe in pregnancy. Metformin occasionally may cause side effects (heartburn, nausea, flatulence) but these effects are lessened if you take the tablet with the first mouthful of food as instructed by the doctor.

Insulin (injection)

You may need additional insulin to control your blood glucose levels. This has to be given by injection into the skin. There are different types of insulin regimens and the medical obstetric team will explain which one is best for you.

If you need insulin the Diabetes Specialist Nurse /Midwife will show you how to inject insulin so that you feel safe and confident to do it on your own at home.

What happens once my baby is born?

Your blood glucose should return to normal post birth. You may need advice from the healthcare team around reducing medications.

Post delivery

Your baby’s blood glucose will need to be monitored post-delivery for a minimum of 24 hours but you may need to stay in hospital longer. This is to check that your baby’s blood glucose is not dropping too low, this is called neonatal hypoglycaemia. Your baby will need to be fed quite soon after delivery and then 3 – 4 hourly, their blood glucose levels will checked regularly before each feed during this time.

Postnatal care

You should be offered a fasting blood glucose test 6 weeks after the delivery of your baby, and a further blood test (called the HbA1c test) 3 months after delivery to check that your blood glucose levels have returned to normal. These tests will be performed at your GP surgery. It is very important that you book this test soon after you have had your baby.

Having gestational diabetes increases your risk of developing diabetes later on in life; therefore it is important to continue to follow a healthy diet and lifestyle and aim to maintain a healthy weight after the birth of your baby. You should have an annual HbA1c to screen for diabetes now you have had gestational diabetes. Speak with your health care team to see what support is available to you.

Speak to GP regarding referral to Diabetes Prevention Programme.


Check your blood glucose regularly

Regular monitoring of blood glucose helps you and your health care team to ensure you and your baby are staying healthy.

Dietary changes

  • Control carbohydrate portions – Aim for salad/ vegetables ½ plate, ¼ protein and ¼ carbohydrate
  • Aim 20-50g carbohydrate per meal
  • Choose unprocessed, higher fibre carbohydrates and avoid/limit refined carbohydrates

Stay active

Even a 10-15 minute walk before a blood glucose check can help to lower your blood glucose levels.



Take medications as prescribed

Your medical team will monitor you and may suggest medications to help control your blood glucose.

This leaflet was produced by the Maternity Services Department, Hull University Teaching Hospitals NHS Trust and will be reviewed in April 2026 (3 years following publication).

General Advice and Consent

Most of your questions should have been answered by this leaflet, but remember that this is only a starting point for discussion with the healthcare team.

Consent to treatment

Before any doctor, nurse or therapist examines or treats you, they must seek your consent or permission. In order to make a decision, you need to have information from health professionals about the treatment or investigation which is being offered to you. You should always ask them more questions if you do not understand or if you want more information.

The information you receive should be about your condition, the alternatives available to you, and whether it carries risks as well as the benefits. What is important is that your consent is genuine or valid. That means:

  • you must be able to give your consent
  • you must be given enough information to enable you to make a decision
  • you must be acting under your own free will and not under the strong influence of another person

Information about you

We collect and use your information to provide you with care and treatment. As part of your care, information about you will be shared between members of a healthcare team, some of whom you may not meet. Your information may also be used to help train staff, to check the quality of our care, to manage and plan the health service, and to help with research. Wherever possible we use anonymous data.

We may pass on relevant information to other health organisations that provide you with care. All information is treated as strictly confidential and is not given to anyone who does not need it. If you have any concerns please ask your doctor, or the person caring for you.

Under the General Data Protection Regulation and the Data Protection Act 2018 we are responsible for maintaining the confidentiality of any information we hold about you. For further information visit the following page: Confidential Information about You.

If you or your carer needs information about your health and wellbeing and about your care and treatment in a different format, such as large print, braille or audio, due to disability, impairment or sensory loss, please advise a member of staff and this can be arranged.

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