Gestational diabetes is a type of diabetes that affects women during pregnancy. Diabetes is a condition caused by 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 slightly 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 that is first diagnosed during pregnancy. There are two other types of diabetes:
- type 1 diabetes - when the body produces no insulin at all (often referred to as insulin-dependent diabetes, juvenile diabetes or early-onset diabetes)
- type 2 diabetes - when the body doesn't produce enough insulin 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.
How common is gestational diabetes?
It is estimated that two to five in every 100 women giving birth has diabetes. Most of these women have gestational diabetes, and some have type 1 or type 2 diabetes.
It is estimated that gestational diabetes affects 12% of pregnant women.
Gestational diabetes can often be controlled with diet and exercise. One or two women in every 10 with gestational diabetes will require medication to control their blood glucose levels (see Gestational diabetes - treatment).
If gestational diabetes is not detected and controlled, it can increase the risk of birth complications, such as shoulder dystocia (when the baby's shoulder gets stuck during the birth). It can also lead to babies being large for their gestational age. See Gestational diabetes - complications for more information about the risks of this condition.
In most cases, gestational diabetes develops in the second or third trimester (from week 14 of the pregnancy to the birth) and 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 is usually diagnosed during routine screening (see Gestational diabetes - diagnosis) before it causes any symptoms. But often, gestational diabetes will not cause any symptoms at all.
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
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).
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 and progesterone. These hormones make your body insulin-resistant, which means that 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 have slightly higher than normal levels of glucose in their blood and their body cannot produce enough insulin to transport it all into the cells. This is known as gestational diabetes.
You may be at increased risk of gestational diabetes if:
- your body mass index (BMI) is more than 25
- 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 - for example, one of your parents 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)
Every pregnant woman should be offered a screening test for gestational diabetes. Screening identifies apparently healthy people who may be at increased risk of a condition, such as diabetes. You can then be offered information, further tests and treatment to reduce the risk of complications from that condition.
You may be screened for gestational diabetes at your booking appointment. This is usually a long antenatal appointment with your midwife or GP, which takes place around weeks 8-12 of your pregnancy. See Pregnancy Care for more information about your care during pregnancy.
At this time, your GP 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. See Gestational diabetes - causes for a full list of the 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) or a random blood glucose test. These test the amount of glucose (sugar) in a sample of blood taken from a vein in your arm.
A random glucose blood test may involve having one or several samples of blood tested to see if your blood glucose levels are as expected, or if they vary widely.
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 every half an hour for two hours, to see how your body is dealing with the glucose.
If you do not have gestational diabetes, you may be asked to return to have another blood test around weeks 24-28.
If you do have gestational diabetes, you will be given advice about how to control and monitor your blood glucose levels
Previous gestational diabetes
If you have had gestational diabetes in a previous pregnancy but the oral glucose tolerance test (OGTT) does not detect it at your booking appointment, you may be instructed in how to self-monitor your blood glucose.
This is usually done by pricking the end of your finger and testing a drop of the blood. See testing your glucose levels for more information on how to do this.
Alternatively, you may be asked to return for another OGTT at around:
- weeks 16-18 of the pregnancy
- week 28 of the pregnancy
The schedule of these appointments may vary depending on the procedures in your area.
If you have gestational diabetes, you will be advised about monitoring and controlling your blood glucose (sugar) levels.
For at least 8 out of 10 women, changing your diet and increasing the amount of exercise you do will be enough to control your gestational diabetes. One or two women in every 10 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 GP or midwife will discuss with you how to test your own blood glucose levels. They will also explain to you 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 (about 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.
You may be advised to change your diet to control your gestational diabetes. In some cases, you may be referred to a dietitian (a healthcare professional who specialises in nutrition) to advise you about a special diet.
Some dietary advice that you may be given is explained below.
You may 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 type of fish you should avoid, for example, eating too much tuna.
Aim to eat a balance of polyunsaturated fats 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
- sunflower, olive and vegetable oil
- spreads that are made from sunflower, olive and vegetable oils
Low GI carbohydrates
You may be advised to choose carbohydrates with a low glycaemic index (GI). The GI ranks food based on how they affect blood sugar levels. Low GI foods are absorbed into the bloodstream slowly, keeping blood sugar levels more stable. High GI foods are absorbed quickly and cause blood sugar levels to rise.
Examples of low GI carbohydrates include:
- pasta made from durum wheat
- sweet potatoes
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 GP or midwife will advise you 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 or midwife will advise you 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.
You can use the healthy weight calculator to work out your BMI - but remember to use your pre-pregnancy weight.
If diet and exercise have not effectively controlled your gestational diabetes after around two weeks, you may be prescribed medication. The timing may vary depending on your glucose levels.
You may also be prescribed medication if an ultrasound scan (when high-frequency sound waves are used to create an image of your womb) suggests that your unborn baby is large for their age.
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:
- rapid-acting insulin analogues (aspart or lispro)
- oral hypoglycaemic agents (metformin or glibenclamide) are used on rare occasions
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 to have insulin injections to ensure that 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:
- regular insulin - this is normally injected before meals and lasts up to eight hours
- rapid-acting insulin analogues (aspart or lispro) - these are normally injected before or just after meals; they work quickly but do not last very long
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:
- blood glucose before going to bed at night
- fasting blood glucose (after you have not eaten for around eight hours - normally first thing in the morning)
- blood glucose about one hour after every meal
If your blood glucose falls too low, you may have hypoglycaemia (see the box, left).
Oral hypoglycaemic agents
In very rare cases you may be prescribed oral hypoglycaemic agents alongside or instead of insulin. These are medicines that 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.
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 their age. Because of this, you may be offered extra antenatal appointments so that 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 every week 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)
- tests of your baby's wellbeing every week from week 38 of the pregnancy; for example, monitoring your baby's heart rate
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, or by a hormone drip into your arm.
You can wait for labour to start naturally as long as it is safe to do so.
If your baby is large for its gestational age (macrosomic), then your GP or midwife should discuss the birth options with you.
You should be advised to give birth at a hospital where healthcare professional 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 at 4 to 7 mmol/l. Around two to four hours after the birth, your newborn baby's blood glucose will also be measured.
You should have the oral glucose tolerance test repeated 6 to 12 weeks after delivery of your baby. You are at a long term risk of developing diabetes and so you should continue to follow a healthy lifestyle with regular testing for diabetes
After you have given birth, any medication you were on to control your blood glucose will be stopped. Your blood glucose level will be tested to make sure that 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 glucose (hyperglycaemia), which could be a sign your diabetes has returned. These are:
- increased thirst
- the need to urinate frequently
Your fasting blood glucose will be measured (after you have not eaten for eight hours – normally first thing in the morning) at your six-week postnatal check.
This will then be measured once a year to make sure you do not develop diabetes.
Hypoglycaemia is an abnormally low level of glucose in the blood. You may be at risk of hypoglycaemia if you are using medication to control your gestational diabetes.
Be informed of the risks of hypoglycaemia, and learn how to recognise the symptoms, such as:
- feeling hungry
- trembling or shakiness
- anxiety or irritability
- going pale
If hypoglycaemia is not treated it may lead to unconsciousness because there is not enough glucose for the brain to function normally.
The immediate treatment of hypoglycaemia is to have some sugary food or drink, such as:
- glucose tablets
- fruit juice
You may be given a concentrated glucose solution (drink) to keep on hand in case you have hypoglycaemia.
See the Health A-Z topic about Hypoglycaemia for more information.
Gestational diabetes can cause complications for both you and your baby. If your blood glucose (sugar) level is effectively controlled throughout your pregnancy, you will reduce the risk of these complications.
Gestational diabetes may increase the risk of:
- pre-eclampsia - a condition that causes high blood pressure in pregnant women
- 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)
- needing to induce labour - when medication is used to start labour artificially
- premature birth (see below)
- macrosomia (see below)
- 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
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. For more information, see the Royal College of Obstetricians and Gynaecologists: shoulder dystocia.
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). See the Health A-Z topic about Type 2 diabetes for more information about this condition.
Therefore, it is very important that your blood glucose is monitored after the birth to ensure that it returns to normal.
Your baby may also be at greater risk of developing these conditions in later life:
- obesity (having a body mass index of more than 30)
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 GP if you are planning another pregnancy. They may arrange for you to monitor your own blood glucose from the early stage of your pregnancy. For more information on diagnosing and monitoring high blood glucose
You can monitor your own blood glucose levels using a simple finger prick 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 GP 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.