Gestational Diabetes Mellitus (GDM)

Patient Leaflets Team

  • Reference Number: HEY-816/2019
  • Departments: Maternity Services
  • Last Updated: 28 February 2019


This leaflet has been produced to give you general information about your condition.  Most of your questions should be answered by this leaflet.  It is not intended to replace the discussion between you and your doctor, but may act as a starting point for discussion.  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. Glucose comes from the digestion of carbohydrate foods such as bread, rice, potatoes, cereals, pasta, fruit and sugar. Your liver also makes glucose. We need glucose to live, as it is our main source of energy. Our body is made of cells. Insulin is a hormone that acts like a key to unlock these cells to allow glucose to enter. This glucose is then used or stored as energy by the body. Insulin therefore helps to lower blood glucose levels and to keep them in the normal range.

During pregnancy your body needs more insulin than usual. This is because the placenta releases hormones which make your body more resistant to insulin. In most women the body can produce enough insulin to overcome this resistance. However in some women they are not able to produce enough insulin and therefore blood glucose levels rise to above normal levels.

What are the risk factors?

  • Previous gestational diabetes.
  • 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.

How is GDM diagnosed?

GDM is diagnosed following an Oral Glucose Tolerance Test (OGTT). GDM is usually confirmed if either of the blood tests during the OGTT shows higher than normal glucose levels.

NICE clinical guidelines state that GDM is diagnosed if:

  • fasting plasma glucose level of 5.6mmol/l or above.
  • or a 2 hour plasma glucose level of 7.8mmol/l or above.

If you have had GDM in a previous pregnancy you may be have just been asked to start self-monitoring early on in this pregnancy rather than have an OGTT.

What are the risks of GDM?

The most common problem associated with GDM is your baby growing too big in your uterus (womb). This is called macrosomia. This is because the growing baby is receiving too much glucose via your placenta. This may cause problems with delivery as the baby grows too large to deliver safely through the vagina. This will mean that your baby may need to be delivered by caesarean section. You may be offered additional scans during pregnancy to assess the growth of your baby. The obstetrician will discuss with you the risks and benefits of delivery either normally (vaginally) or by caesarean section so that you have an informed choice about the safest way to deliver your baby.

GDM also increases the risk of:

  • Stillbirth
  • Raised blood pressure during the pregnancy (pre-eclampsia)
  • Preterm (early) labour

These risks can be significantly reduced with the support of your healthcare team. You will be asked to monitor your blood glucose levels, attend regular check-ups and be offered advice around your diet, weight and activity levels.

What happens next?

Blood glucose monitoring

You are required to blood glucose monitor at least 5 times per day to check blood glucose levels. You are required to monitor pre breakfast, 1 hour post breakfast, pre lunch, pre evening meal and 1 hour post evening meal.

You should aim to keep the levels less than 5.5 mmol/L before meals and less than 8mmol/L 1 hour after a meal. Even if your blood glucose readings are all in target it is important that you continue to monitor your blood glucose throughout your pregnancy.

You will be provided with replacement strips and lancets for your monitor by your GP together with a special yellow sharps bin for disposing of the used lancet needles. These will then be disposed of on request by the local council. Telephone (01482) 300300 for Hull, or (01482) 393939 for East Riding.

Dietary management

All carbohydrates are digested into glucose therefore, the more carbohydrate you eat the higher your blood glucose levels will rise. If your blood glucose readings are above the pre and post meal targets the key is to:

  • reduce your carbohydrate portions
  • spread your carbohydrates more evenly throughout the day
  • choose better types of carbohydrate

Which foods contain carbohydrate?

Quantities of carbohydrate at each meal

If you are struggling to achieve the pre and post meal blood glucose targets it may be worth reducing the amount of carbohydrate you are eating at each meal. Try to aim for the following amount of carbohydrate at each meal:

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).

Be careful with the sauces added to main meals as these may increase the carbohydrate content of the meals you are having, especially if they are milk based or have added sugar, examples include white sauce / béchamel sauce, sweet and sour sauce.

If you are hungry between meals you could try 1 of the following 10-15g carbohydrate snacks mid-morning, mid-afternoon and at supper:

  • piece of fruit – fun-size 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

You can also consider trying increasing the protein (e.g. lean meat, fish, lentils, pulses), salad and vegetables at meals as these do not affect your blood glucose levels.

Type of carbohydrate – Low Glycaemic index (GI)

Glycaemic index (GI) is a ranking of carbohydrate – containing foods based on their effect on blood glucose levels. Choosing low glycaemic index (GI) foods can help to control blood glucose levels as these foods are absorbed more slowly.

Lower glycaemic index foods include oat based cereal such as porridge and muesli, multigrain/seeded/granary or rye bread, pasta, noodles, basmati rice, quinoa, beans, lentils, milk, yoghurt and most fruits and vegetables. However if you are basing your meal on low GI foods you still need to be aware that the quantity chosen will have the biggest effect on your blood glucose readings so follow the guidance regarding quantities at meals as above.

Avoid sugar rich drinks

During pregnancy, women often experience a craving for fresh fruit juice and fizzy drinks. These are both very high in carbohydrate therefore you could consider changing to diet fizzy drinks and reduce the amount of fruit juice you are drinking.

Diabetic food products are not recommended as they can have a laxative effect.


You are still able to safely exercise during pregnancy. Regular exercise is important in helping keep your blood glucose levels within the targets, for example walking for 30 minutes after a meal. Exercise will also help in preventing excessive weight gain.

Moderate intensity activity will not harm your baby. At least 30 minutes per day of moderate intensity activity is recommended. 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. Recreational exercise such as swimming or brisk walking and strength conditioning exercise is safe and beneficial. The aim is to stay fit, rather than to reach peak fitness.

If you have not exercised routinely aim to begin with no more than 15 minutes of continuous exercise, three times per week, increasing gradually to 30 minutes per day. If you have exercised regularly before pregnancy, you should be able to continue with no adverse effects.

Managing your weight

Weight loss is not recommended during pregnancy. However making small changes to your diet and increasing your activity levels whilst you are pregnant to help manage your blood glucose levels can also help to avoid too much weight gain during pregnancy.

Diabetic medicines which may be used in pregnancy

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.

  • if the insulin is cloudy (Insulatard, Humulin I or Insuman Basal), tip the pen 10 times and roll it 10 times to mix the insulin
  • before injecting, check the pen is working by doing an air shot of 2 units of insulin
  • inject at 90o right angle and hold down the button for at least 10 seconds
  • inject into your outer thighs, buttocks or abdomen and remember to rotate your injection sites
  • take the needle out slowly, and place the needle in your sharps box

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.

Should you require further advice on the issues contained in this leaflet or have concerns about your pregnancy, please contact us via telephone:

  • Labour & Delivery (01482) 604390 & 604490
  • Antenatal Day Unit (01482) 382729
  • Antenatal Clinic Reception Desk (01482) 604386
  • Diabetes Specialist Midwife / Nurse (01482) 675391
  • Diabetes Specialist Dietitian (01482) 675373

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