What is gestational diabetes?
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 have higher than normal levels of glucose in their blood and their body cannot produce enough insulin to transport it all into the cells. This means that the level of glucose in the blood rises.
Types of diabetes
Gestational diabetes is diabetes 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 do not react to insulin (insulin resistance)
See the relevant links above for women who already had diabetes before they became pregnant.
Gestational diabetes can be controlled with diet and exercise. However, some women with gestational diabetes will need medication to control blood glucose levels. Read more about how gestational diabetes is treated.
If gestational diabetes is not detected and controlled, it can increase the risk of birth complications, such as babies being large for their gestational age (Macrosomia). Read about the complications of gestational diabetes for more information about the risks of this and related conditions.
In most cases, gestational diabetes 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.
Gestational diabetes symptoms
Gestational diabetes is often diagnosed during routine screening. It sometimes does not cause any symptoms.
However, high blood glucose (hyperglycaemia) can cause some symptoms, including:
- being thirsty
- having a dry mouth
- needing to urinate frequently
- recurrent infections, such as thrush (a yeast infection)
- blurred vision
See the topic about Hyperglycaemia for more information about this.
Gestational diabetes causes
Diabetes is a condition where there is too much glucose (sugar) in the blood.
The amount of glucose in your 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 that the insulin does not work properly.
When you eat, your digestive system breaks down food and the nutrients are absorbed into your bloodstream. Normally, insulin is produced to take any glucose out of your blood and move it into your cells. The glucose in your cells is then broken down to produce 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.
In order to cope with the increased amount of glucose in your blood, your body should produce more insulin. However, some women 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 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)
Gestational diabetes diagnosis
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 booking appointment. This is the first antenatal appointment with your midwife or doctor, which takes place around weeks 8-12 of your pregnancy.
At this time, your doctor or midwife will find out if you are at increased risk of gestational diabetes. They will do this by asking about any risk factors that may affect you, such as whether you have a family history of diabetes.
Read about the causes of gestational diabetes for a full list of risk factors you will be asked about.
If any one of these risk factors applies to you, you will be offered a test for gestational diabetes.
Gestational diabetes is detected by using an oral glucose tolerance test (OGTT), usually at 24-28 weeks. For an OGTT, a sample of your blood will be tested, then you will be given a glucose drink. Another sample of blood will then be taken two hours later to see how your body is dealing with the glucose.
If you have had gestational diabetes in a previous pregnancy, the OGTT will be carried out at 16-18 weeks, followed by a repeat OGTT at 28 weeks if the first test is normal.
Read more about how gestational diabetes is treated.
Gestational diabetes treatment
If you have gestational diabetes, you will be advised about monitoring and controlling your blood glucose (sugar) levels.
For many women, changing diet and more exercise will be enough to control your gestational diabetes. Some women will need medication.
In addition, you will be taught how to monitor your blood glucose, and your unborn baby will be closely monitored.
Monitoring blood glucose
Your doctor, midwife, or diabetes team will discuss with you how to test your blood glucose levels. They will also explain how blood glucose is measured, and 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 hour 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 below, under Medications), you may need to test your blood glucose before going to bed at night.
Read about testing your glucose levels for more information about how to do this.
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) to advise on a special diet.
Some advice you may be given is explained below.
Don't skip meals. By eating regular, balanced meals which include a starchy carbohydrate with a low Glycaemic Index (GI) you can absorb carbohydrate more slowly helping 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 – with low GI foods absorbed into the bloodstream slowly, and high GI foods 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. Think variety to get the full benefits of low GI foods.
Eat more fruit and vegetables
Aim for at least five portions a day to provide vitamins, minerals and fibre but keep to one portion of fruit at a time. And try to include beans and lentils such as kidney beans, butter beans, chickpeas or red and green lentils.
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 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 should avoid, for example, eating too much 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.
Your doctor, 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 doctor, midwife, or diabetes team will advise about the safest way to exercise during pregnancy.
If your body mass index (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) every 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 around 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 and glibenclamide 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 because if you swallowed it, the enzymes (proteins that speed up and control chemical reactions in the body) in your stomach would digest it like a food, and it would not be effective. If you need insulin injections, you will be shown:
- how and when to inject yourself
- how to store your insulin and dispose of your needles properly
Insulin comes in several different preparations. You may be prescribed:
- Rapid acting insulin analogues (aspart or lispro) – these are normally injected before or just after meals; they work quickly but do not last long
- Basal insulin (insulatard or lantus) – 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 hour 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.
Oral hypoglycaemic agents
In some cases, you may be prescribed oral hypoglycaemic agents alongside or instead of insulin. These are medicines you swallow to lower the level of glucose in your blood. The two that can be used during pregnancy are:
- glibenclamide (from week 11 of the pregnancy)
Both metformin and glibenclamide can cause side effects, including:
- nausea (feeling sick)
- diarrhoea (passing loose, watery stools)
As with insulin, if you are using glibenclamide you may be at risk of hypoglycaemia (see box, left). This does not usually happen with metformin unless it is used in combination with insulin or glibenclamide.
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 (the fluid that surrounds them in the womb)
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.
This can be done by inducing labour. This is when labour is started artificially by inserting a pessary (tablet) or gel into your vagina, and a hormone drip in your arm (read about [inducing labour] for more information).
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 your baby is large for its gestational age (macrosomic), then your doctor or midwife should discuss the birth options with you.
Normal delivery is usually still possible but will depend on the size of the baby.
You should give birth at a hospital where healthcare professionals trained in resuscitating newborn babies are available 24 hours a day.
During labour and the birth, your blood glucose will be measured every hour and kept between 4 to 7 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.
Around two to four hours after the birth, your newborn baby’s blood glucose will also be measured, this will usually be before the baby’s second feed.
Diabetes blood testing
You can monitor your own blood glucose levels using a simple finger prick test or a urine test.
Finger prick testing
This is what you will need to do it independently:
- blood testing strips
- blood glucose meter
- finger pricking device
- blood glucose monitoring diary
- sharps box for disposal of sharps
These are available from your doctor or hospital.
- Before doing a finger prick test, make sure you have all your equipment in a clean dry place.
- Wash your hands and rinse well with warm water (dirty hands can contaminate a blood sample and give an inaccurate result).
- Choose your finger and massage it to improve blood circulation.
- Pricking the fleshy part of your finger can hurt. Instead prick the side of the finger away from the thumb. Squeeze your finger gently to obtain a drop of blood.
- Apply the drop of blood to the testing strip. The meter will automatically read the result.
- Note the result in your diary.
Gestational diabetes complications
If gestational diabetes goes undetected, or is not managed effectively, it can cause complications for both you and your baby.
Controlling your blood glucose (sugar) levels throughout your pregnancy reduces the risk of complications.
Gestational diabetes may increase the risk of:
- placental abruption – the placenta (the organ that links the pregnant woman’s blood supply to her unborn baby’s) starts to come away from the wall of the womb (uterus). This may cause vaginal bleeding and/or constant abdominal pain
- needing to induce labour – when medication is used to start labour artificially
- premature birth
- trauma during the birth – to yourself and your baby
- neonatal hypoglycaemia – your newborn baby has low blood glucose, which can cause poor feeding, blue-tinged skin and irritability
- perinatal death – the death of your baby around the time of the birth
- development of obesity and/or diabetes later in the baby's life
Gestational diabetes can cause premature birth (your baby being born before week 37 of the pregnancy). This can lead to further complications for your baby, such as:
- respiratory distress syndrome – your baby’s lungs are not fully developed and cannot provide enough oxygen to the rest of their body
- jaundice – your baby’s skin turns yellow when a waste product called bilirubin builds up in the blood
Gestational diabetes increases the risk of your baby being large for its gestational age, i.e. weighing more than 4kg (8.8lbs). This is known as macrosomia.
Macrosomia occurs during the pregnancy because the excess glucose in the mother’s blood is passed to the foetus (unborn baby). This causes the foetus to produce insulin (a hormone) that allows glucose to enter the cells, which results in growth.
Macrosomia can lead to a condition called shoulder dystocia. This is when your baby’s head passes through your vagina, but your baby’s shoulder gets stuck behind your pelvic bone (the ring of bone that supports your upper body, also called the hip bones).
Shoulder dystocia can be dangerous as your baby may not be able to breathe while they are stuck. It is estimated to affect 1 in 200 births.
After having gestational diabetes, you are around seven times more likely to develop type 2 diabetes than women who have had a normal pregnancy.
Type 2 diabetes is when your body does not produce enough insulin, or the body’s cells do not react to the insulin (insulin resistance). read about type 2 diabetes for more information about this condition.
Therefore, it is important your blood glucose is monitored after the birth to check whether or not it returns to normal.
Your baby may also be at greater risk of developing these conditions in later life:
After having gestational diabetes, you are at increased risk of having gestational diabetes in any future pregnancies.
It is very important to speak to your doctor if you are planning another pregnancy. They may arrange for you to monitor your own blood glucose from the early stage of your pregnancy. Read about diagnosing gestational diabetes for more information.