It can occur at any stage of pregnancy, but is more common in the second half.
It occurs if your body cannot produce enough insulin – a hormone that helps control blood sugar levels – to meet the extra needs in pregnancy.
Gestational diabetes can cause problems for you and your baby during and after birth. But the risk of these problems happening can be reduced if it's detected and well managed.
Any woman can develop gestational diabetes during pregnancy, but you're at an increased risk if:
If any of these apply to you, you should be offered screening for gestational diabetes during your pregnancy.
Gestational diabetes doesn't usually cause any symptoms.
Most cases are only picked up when your blood sugar level is tested during screening for gestational diabetes.
Some women may develop symptoms if their blood sugar level gets too high (hyperglycaemia), such as:
But some of these symptoms are common during pregnancy anyway and aren't necessarily a sign of a problem. Speak to your midwife or doctor if you're worried about any symptoms you're experiencing.
Most women with gestational diabetes have otherwise normal pregnancies with healthy babies.
However, gestational diabetes can cause problems such as:
Having gestational diabetes also means you're at an increased risk of developing type 2 diabetes in the future.
During your first antenatal appointment at around weeks 8 to 12 of your pregnancy, your midwife or doctor will ask you some questions to determine whether you're at an increased risk of gestational diabetes.
If you have one or more risk factors for gestational diabetes – see Who's at risk, above – you should be offered a screening test.
The screening test used is called an oral glucose tolerance test (OGTT), which takes about two hours.
It involves having a blood test taken in the morning when you've had nothing to eat or drink (except water) overnight. You're then given a glucose drink.
After resting for two hours, another blood sample is taken to see how your body is dealing with the glucose.
The OGTT is done when you're between 24 and 28 weeks pregnant. If you've had gestational diabetes before, you'll be offered an OGTT earlier in pregnancy soon after your booking visit, and another OGTT at 24 to 28 weeks if the first test is normal.
Alternatively, it may be suggested that you start testing your blood sugar yourself using a finger-pricking device in the same way as you did during your previous episode of gestational diabetes.
In women with gestational diabetes, the chances of having problems with the pregnancy can be reduced by controlling blood sugar levels.
You'll be given a blood sugar testing kit so you can monitor the effects of treatment.
Blood sugar levels can be reduced by changes in diet and exercise. But the majority of women will need medication as well if changes in diet and exercise don't reduce blood sugar enough. This may be tablets or insulin injections.
You'll also be more closely monitored during your pregnancy and birth to check for any potential problems.
If you have gestational diabetes, it's best to give birth before 41 weeks. Induction of labour or a caesarean section may be recommended if labour doesn't start naturally by this time.
Earlier delivery may be recommended if there are concerns about your or your baby's health or if your blood sugar levels haven't been well controlled.
Read more about how gestational diabetes is treated.
Gestational diabetes normally goes away after birth. But women who've had it are more likely to develop:
You should have a blood test to check for diabetes 6 to 13 weeks after giving birth, and every year thereafter if the result is normal.
See your GP if you develop symptoms of high blood sugar, such as increased thirst, needing to pee more often than usual, and a dry mouth – don't wait until your next test.
You should have the tests even if you feel well, as many people with diabetes don't have any symptoms.
You'll also be advised about things you can do to reduce your risk of developing diabetes, such as maintaining a healthy weight, eating a balanced diet and exercising regularly.
Some research has suggested that babies of mothers who had gestational diabetes may be more likely to develop diabetes or become obese later in life.
If you've had gestational diabetes before and you're planning to get pregnant, make sure you get checked for diabetes. Your GP can arrange this.
If you do have diabetes, you should be referred to a diabetes pre-conception clinic for support to ensure your condition is well controlled before you get pregnant.
Read more about diabetes in pregnancy.
If you have an unplanned but wanted pregnancy, talk to your GP and tell them you had gestational diabetes in your previous pregnancy.
If tests show you don't have diabetes, you'll be offered screening earlier in pregnancy soon after your booking visit, and a repeat screening test at 24 to 28 weeks if the first test is normal.
Alternatively, it may be suggested that you start testing your blood glucose yourself using a finger-pricking device in the same way as you did during your previous gestational diabetes.