Gestational diabetes is a type of diabetes that affects women during pregnancy. Diabetes is a condition where there is too much glucose (sugar) in the blood.
Normally, the amount of glucose in the blood is controlled by a hormone called insulin.
However, during pregnancy, some women develop higher than normal levels of glucose in their blood, which insulin can't bring under control.
Gestational diabetes usually develops in the third trimester (after 28 weeks) and usually disappears after the baby is born. However, women who develop gestational diabetes are more likely to develop type 2 diabetes later in life.
Types of diabetes
Gestational diabetes is first diagnosed during pregnancy. The two other main types of diabetes are:
- type 1 diabetes – when the body produces no insulin at all (often referred to as juvenile diabetes or early-onset diabetes)
- type 2 diabetes – when the body doesn't produce enough insulin and/or the body’s cells don't react to insulin (insulin resistance)
Symptoms of gestational diabetes
Gestational diabetes often doesn't cause any symptoms. This means you may be screened for the condition at your first antenatal appointment by a venous glucose sample, at around weeks 8-12 of pregnancy.
If you are at increased risk of gestational diabetes you will be offered a full test, which takes place during weeks 24-28 of pregnancy.
High blood glucose (hyperglycaemia) can cause some symptoms, including:
- a dry mouth with increased thirst
- needing to urinate frequently, especially at night
- recurrent infections, such as thrush (a yeast infection)
- blurred vision
How common is gestational diabetes?
Gestational diabetes is a common condition, and up to 18 in every 100 women giving birth in England and Wales may be affected.
Treating gestational diabetes
Gestational diabetes can be controlled with diet and exercise. However, some women will need medication to keep their blood glucose levels under control.
If gestational diabetes is not detected and treated, it can increase the risk of birth complications for both the mother and baby.
Causes of gestational diabetes
Diabetes is caused by too much glucose (sugar) in the blood.
The amount of glucose in the blood is controlled by a hormone called insulin, which is produced by the pancreas (a gland behind the stomach).
Diabetes is caused either by insufficient insulin being produced, or the body becoming resistant to insulin, which means the insulin doesn't work properly.
When you eat, your digestive system breaks down food and the nutrients are absorbed into your bloodstream.
The hormone insulin is produced and acts like a key, opening the cells to allow glucose to move into the body for energy.
During pregnancy, your body produces a number of hormones (chemicals), such as oestrogen, progesterone and human placental lactogen (HPL). These hormones make your body insulin-resistant, which means your cells respond less well to insulin and the level of glucose in your blood remains high.
The purpose of this hormonal effect is to allow the extra glucose and nutrients in your blood to pass to the foetus (unborn baby), so it can grow.
To cope with the increased amount of glucose in your blood, your body should produce more insulin. However, some women either cannot produce enough insulin in pregnancy to transport the glucose into the cells, or their body cells are more resistant to insulin. This is known as gestational diabetes.
You may be at increased risk of gestational diabetes if:
- your body mass index (BMI) is 30 or more – you can use the healthy weight calculator to work out your BMI
- you have previously had a baby who weighed 4.5kg (10lbs) or more at birth – the medical term for a birth weight of more than 4kg (8.8lbs) is macrosomic
- you had gestational diabetes in a previous pregnancy
- you have a family history of diabetes – one of your parents or siblings has diabetes
- your family origins are South Asian (specifically India, Pakistan or Bangladesh), black Caribbean or Middle Eastern(specifically Saudi Arabia, United Arab Emirates, Iraq, Jordan, Syria, Oman, Qatar, Kuwait, Lebanon or Egypt)
Diagnosing gestational diabetes
Every pregnant woman with one or more risk factors should be offered a screening test for gestational diabetes.
Screening identifies otherwise healthy people who may be at increased risk of a condition, such as diabetes. You can then be offered information and further tests to determine whether you have the condition.
You may be screened for gestational diabetes at your first antenatal appointment with your midwife or GP, which takes place around weeks 8-12 of your pregnancy.
At this time, your GP or midwife will find out if you are at increased risk of gestational diabetes. They will ask about any known risk factors for gestational diabetes, such as whether you have a family history of diabetes.
If any of these risk factors apply to you, you'll be offered a blood test to check your glucose levels. This may also include a glucose tolerance test (GTT).
Glucose tolerance test (GTT)
A GTT takes place during weeks
24-28 of pregnancy.
This involves a morning blood test, before you have eaten breakfast. You are then given a glucose drink, and another blood sample is taken two hours later to see how your body is dealing with the glucose.
If you had gestational diabetes in a previous pregnancy, the GTT will be carried out at weeks 16-18 of pregnancy – or sooner, if indicated by the first blood glucose sample. This is followed by a repeat GTT at 28 weeks, if the first test is normal.
Treating gestational diabetes
If you have gestational diabetes, you will be advised about monitoring and controlling your blood glucose (sugar) levels.
For many women, changing diet and exercising more will be enough to control your gestational diabetes. Some women will need medication.
In addition, you'll be taught how to monitor your blood glucose, and your unborn baby will be closely monitored.
Monitoring blood glucose
Your GP, midwife or diabetes team will tell you how to test your blood glucose level and explain what level you should be aiming for.
Blood glucose levels are usually measured in terms of the amount of millimoles of glucose in one litre of blood. A millimole is a measurement that defines the concentration of glucose in your blood. The measurement is expressed as millimoles per litre, or mmol/l for short.
Your individual mmol/l target will be set for you. This may include a target for your:
- fasting blood glucose (after you have not eaten for around eight hours – normally first thing in the morning)
- postprandial blood glucose (one or two hours after you have eaten)
You will be advised when and how often you need to test your blood glucose. You may need to test your fasting blood glucose and your blood glucose after every meal throughout your pregnancy.
If your diabetes is being treated with insulin (see the Medications section below), you may need to test your blood glucose before going to bed at night.
You may be advised to change your diet to control your gestational diabetes. You should be referred to a dietician (a healthcare professional who specialises in nutrition), who can advise on a special diet.
Some advice you may be given is explained below.
Don't skip meals. By eating regular, balanced meals that include a starchy carbohydrate with a low glycaemic index (GI) you can absorb carbohydrate more slowly, which helps to keep your blood glucose levels stable between meals.
Choose from pasta, basmati or easy cook rice; grainy breads such as granary, pumpernickel and rye; new potatoes, sweet potato and yam; porridge oats, All-Bran and natural muesli. High-fibre varieties of starchy foods will also help your digestive system and prevent constipation.
The GI ranks food based on its effect on blood sugar levels. Low-GI foods are absorbed into the bloodstream slowly, while high-GI foods are absorbed quickly, causing blood sugar levels to rise.
Don't get obsessed with GI ratings. Aim for a balanced and appealing diet, which you can keep to over time. To get the full benefits of low-GI foods, aim for as much variety as possible.
Eat more fruit and vegetables
Aim for at least five portions of fruit and vegetables a day, as these provide vitamins, minerals and fibre. However, keep to one portion of fruit at a time and no more than three fruit portions a day. Fruit juice should be avoided.
Try to include beans and lentils, such as kidney beans, butter beans, chickpeas or red and green lentils. Advice and tasty recipes are available from Diabetes UK.
Limit sugar and sugary foods
You don't need to eat a sugar-free diet. Sugar can be used in foods and in baking as part of a healthy diet, but use it sparingly. Drinking sugar-free, no added sugar or diet colas or squashes, instead of sugary versions, can reduce the amount of sugar in your diet.
You may also be advised to choose lean (not fatty) proteins, such as fish. Eat two portions of fish a week, one of which should be oily fish, such as sardines or mackerel. There are some fish you shouldn't eat too much of, such as tuna.
Aim to eat a balance of polyunsaturated and monounsaturated fats. Small amounts of unsaturated fat will keep your immune system (the body’s defence system) healthy and can reduce cholesterol levels (cholesterol is a fatty substance that can build up in your blood and seriously affect your health).
Foods that contain unsaturated fat include:
- nuts and seeds
- spreads made from sunflower, olive and vegetable oils
If your body mass index (BMI) was more than 27 before you became pregnant, you may be advised to reduce the amount of calories in your diet. You can use the healthy weight calculator to work out your BMI – but remember to use your pre-pregnancy weight.
Your GP, midwife or diabetes team will advise how many calories you should eat a day, and the safest way to cut out calories from your diet.
Physical activity lowers your blood glucose level, so regular exercise can be an effective way to treat gestational diabetes. Your GP, midwife or diabetes team will advise on the safest way to exercise during pregnancy.
If your BMI was more than 27 before you became pregnant, you may be advised to take moderate exercise for at least 150 minutes (2 hours and 30 minutes) a week.
This can be any activity that gets you slightly out of breath and raises your heart rate, such as cycling or fast walking.
If diet and exercise have not effectively controlled your gestational diabetes after one to two weeks, you may be prescribed medication. The timing may vary, depending on your glucose levels.
There are several different types of medication available, and the choice will depend on:
- what will most effectively control your blood glucose
- what is acceptable to you
Possible medicines include:
- metformin in tablet form
These are explained in more detail below. These medicines will be stopped immediately after the birth of your baby.
If you are insulin-resistant (your body does not respond to insulin), you may need insulin injections to ensure your body has enough insulin to lower your blood glucose levels.
Insulin must be injected, so if you need to take it you will be shown:
- how and when to inject yourself
- how to store your insulin and dispose of your needles properly
- signs and symptoms of low blood sugar
- driving and DVLA regulations with insulin
Insulin comes in several different preparations.You may be prescribed:
- rapid-acting insulin analogues – these are normally injected before or just after meals; they work quickly, but do not last long
- basal insulin – these are normally injected at bedtime or on waking; they provide the background insulin required to keep blood glucose levels stable between meals
These are safe to use during pregnancy. However, you will need to monitor your blood glucose closely. If you are being treated with insulin, you will need to check your:
- fasting blood glucose (after you have not eaten for around eight hours – normally first thing in the morning)
- blood glucose, one or two hours after every meal
- blood glucose at other times (for instance, if you feel unwell or have been having episodes of hypoglycaemia – low blood glucose)
If your blood glucose falls too low, you may have hypoglycaemia (see the box, left).
Oral hypoglycaemic agents
In some cases, you may be prescribed an oral hypoglycaemic agent called metformin, alongside or instead of insulin. These are medicines you swallow to lower the level of glucose in your blood.
Metformin can cause side effects, including:
- nausea (feeling sick)
- stomach cramps and diarrhoea (passing loose, watery stools)
For a full list of side effects, see the patient information leaflet that comes with your medicine.
Monitoring your unborn baby
If you have gestational diabetes, your unborn baby may be at risk of complications, such as being large for the state of pregnancy. Because of this, you may be offered extra antenatal appointments so your baby can be closely monitored during your pregnancy.
Appointments you may be offered include:
- an ultrasound scan around weeks 18-20 of your pregnancy, to check your unborn baby’s heart for any signs of abnormalities (if your gestational diabetes is diagnosed late into your pregnancy, you may not be offered this scan)
- an ultrasound scan at weeks 28, 32, 36 and regular checks from week 38 of the pregnancy to monitor your baby’s growth and the amount of amniotic fluid (which surrounds them in the womb)
You can wait for labour to start naturally as long as your blood sugars are within normal levels, the ultrasound scans of the baby are normal, and there is no other problem in pregnancy.
If you have gestational diabetes and your baby is growing at a normal rate, you may be offered the chance to start labour (the process of giving birth) after week 38 of pregnancy.
If your baby is large for its gestational age (macrosomic), then your doctor or midwife will discuss the risks and benefits of a casesarean section.
An individualised diabetes birth should be discussed with you at 36-38 weeks.
You should give birth at a hospital where healthcare professionals are available to provide appropriate care for your baby 24 hours a day.
During labour and the birth, your blood glucose will be measured every hour and kept at 4-6 mmol/l. If you have been on insulin during pregnancy, you will be recommended to have an intravenous drip of insulin as well as glucose during labour, to allow careful control of your blood sugar levels.
Caring for your newborn baby
Around two to four hours after the birth, your newborn baby’s blood glucose will also be measured, usually before the baby’s second feed.
If your baby's blood glucose remains very low, they may need to be fed through a tube or given a drip. If your baby is unwell or needs close monitoring, they may be looked after in a neonatal unit.
After you have given birth, any medication you were on to control your blood glucose will usually be stopped immediately. Your blood glucose level will be tested about 6-12 weeks after delivery, to make sure it has returned to normal.
Your weight and waist measurement may be monitored and you should be given advice about diet and exercise.
You should be aware of the symptoms of high blood sugar (hyperglycaemia), which could be a sign your diabetes has returned. These are:
- increased thirst
- the need to urinate frequently
Depending on your glucose levels at diagnosis, you will either have a repeat oral glucose tolerance test (GTT) or your GP will arrange a HbA1c test (a marker of your average blood sugar over the preceding 3 months) at 12 weeks.
An HbA1c will then be measured at least once a year to check whether or not you have developed type 2 diabetes.