Written by:

Dr Tara Masilamani

BMBCh, Ba (Hons)

Dr Masilamani is an Obstetrics and Gynaecology registrar working in the North West London training deanery. Having completed her medical degree at the University of Oxford she has gone on to pursue a career providing care for women at all stages of life, including pregnancy and childbirth.

What is gestational diabetes?

In this article:

  • Who gets gestational diabetes?
  • Symptoms
  • Testing for gestational diabetes
  • Effect on pregnancy
  • Treatment
  • Gestational diabetes in labour
  • Long-term effects
  • Main Points

What is gestational diabetes?

Gestational: related to pregnancy
Diabetes: high blood sugar level due to lower insulin level

Gestational diabetes is when the body is not able to control the level of glucose in the bloodstream during pregnancy. Glucose is the sugar your body uses as energy. It is usually kept within a safe range by a hormone called insulin. Sometimes pregnancy hormones can interfere with insulin so that it doesn’t work as well and, therefore, extra insulin is needed. If the body is not able to respond and produce this extra insulin, pregnancy diabetes will develop.

If your glucose level is too high, it can have negative effects on you and your baby.

Who gets gestational diabetes?

Gestational diabetes is relatively common, affecting approximately 18 in 100 pregnancies. It is more common in the second half of your pregnancy, though rarely it can occur earlier. Although any pregnant woman is at risk of developing diabetes, your risk is higher if you have any of the following:

  • A body mass index (BMI) over 30kg/m2
  • A previous baby weighing more than 4kg (10lbs) at delivery
  • Developed gestational diabetes in a previous pregnancy
  • Parents/siblings with diabetes
  • South Asian, Chinese, African-Caribbean or Middle Eastern ethnic origin


Most women with gestational diabetes will not be aware they have it. This is why it is important to attend if you are asked to be tested for gestational diabetes. If the sugar level is high you may experience:

  • Increased thirst and need to drink more fluids
  • A need to pass urine more frequently
  • Blurred vision
  • Tiredness

Some of these symptoms may just be due to pregnancy and not diabetes. If you have any concerns, please speak to your doctor or midwife.

Testing for gestational diabetes

If you have one or more of the above risk factors, you will be asked to attend for “screening” between 24-28 weeks gestation. Screening is where we look for the disease in a selected group of people. If you have had gestational diabetes in a previous pregnancy, you will be screened at a much earlier stage of pregnancy, usually between 12-18 weeks.

The test is an “oral glucose tolerance test”, or OGTT. It involves having a blood test for glucose in the morning when you haven’t had anything to eat or drink overnight (you may only drink water). Then you are given a glucose drink (Lucozade, for example) and another blood test is done two hours later. If your body can control its sugar levels well, both blood sugar tests will be normal. If one or both of the tests come back as high, then it is likely you have developed pregnancy diabetes. You will be given a finger prick monitor to check your sugar levels at home for a week or two to confirm whether you have the condition.

If you are not invited to a screening, you may still be tested for diabetes if, for example, there is significant glucose in your urine at a clinic appointment, your baby is found to be large, or a scan shows there is a lot of amniotic fluid around your baby.

Effect on pregnancy

Most women with gestational diabetes will have uncomplicated pregnancies and healthy babies. The adverse effects of the condition are directly related to the blood sugar level. Therefore, the better controlled your blood sugar, the lower the risk of all of the complications. Some of the potential effects of a high sugar level include:

Large for gestational age baby, or “macrosomia”
When babies are large, usually more than 4kg at delivery, the risk in labour is higher. This may be because the baby fails to descend into the birth canal appropriately, leading to a failure of progression in labour, and may require a caesarean section or delivery with an instrument (suction cup or forceps). Sometimes the wider shoulders of the baby may get stuck after the head is delivered. This is known as shoulder dystocia, which is an emergency because the umbilical cord supplying the blood to the baby may be blocked during this period. The pressure on the stuck shoulder may also cause breakage to the baby’s bones or nerve damage that may have temporary or permanent effects on the baby’s ability to use that arm. Having a larger baby to deliver also puts the mother at risk of having more extensive vaginal tears and a higher risk of bleeding.

Excessive amniotic fluid or “polyhydramnios”
Too much fluid around the baby can result in pre-term delivery (birth before 37 weeks) or a cord prolapse. A cord prolapse occurs when the waters break and the umbilical cord falls through the cervix and into the vagina, resulting in spasm of the umbilical cord and reduced blood flow to the baby. This requires an emergency caesarean to deliver the baby quickly.

Babies born with low sugar levels or “neonatal hypoglycaemia”
If your sugar levels are continuously high, then this will be the case for the baby too. The baby compensates by producing its own increased level of insulin. When the baby is delivered and removed from the high sugar environment, this may lead to a dramatic reduction in the baby’s own sugar level, leading to hypoglycaemia. This needs correction with scheduled feeding of glucose via a drip. The baby may need to stay in the hospital for a few days or be admitted to the neonatal unit for monitoring. Low glucose levels can have negative effects on the baby’s brain development.

The risk of a stillbirth is increased but it is important to remember that the overall risk is still low.


Because of all of the risks above, it is very important to treat gestational diabetes to control blood sugar levels. The majority of women with pregnancy diabetes will be able to do this with exercise and diet alone. One in five women will need to have treatment either with tablets (metformin) or insulin injections.

You will need to be seen by the obstetric doctors (doctors who look after pregnant women) in order to monitor how well the pregnancy is progressing. They will arrange 1-2 extra scans to check the growth of the baby and the fluid level. They will give you a planned delivery date. Usually the target for delivery is between 38-41 weeks. How early will depend on the treatment you are on and how well the sugars are controlled.

Gestational diabetes in labour

When it comes to delivering your baby, you will need to be in a labour ward. This is because your sugar levels need to be monitored hourly, and the baby will be monitored on an electronic trace, or “CTG”, throughout your labour. If your sugar level is not controlled, you may be given insulin via an intravenous infusion or drip (“sliding scale”). If the baby is large, it is important to have doctors on standby because of the risk of slow labour, shoulder dystocia, vaginal tearing, and bleeding after delivery.

Most women with pregnancy diabetes will have an uncomplicated labour and delivery. After the baby is born, your and your baby’s sugar levels will need to be checked periodically.

Long-term effects

Unfortunately, gestational diabetes puts you at risk of developing type 2 diabetes outside of pregnancy. One in three women will develop type 2 diabetes within five years of delivering their baby. Your GP will check your sugar levels at your routine 6-8 week post-natal appointment and also annually thereafter. Again, type 2 diabetes may not cause any symptoms and you may not be aware if you develop the condition. Therefore, it is important to have this checked every year even if you feel well. To reduce the risk of getting diabetes, it is important to maintain a healthy weight and continue with regular exercise and a healthy diet.

Main Points

  • Gestational diabetes occurs when pregnancy hormones interfere with the mother’s insulin levels and mean her body is unable to control the level of glucose (sugar) in the blood.
  • Gestational diabetes is a relatively common condition, affecting 18% of pregnancies.
  • There are several factors, including your BMI and ethnic origin, that will affect your likelihood developing the condition.
  • High sugar levels can lead to several symptoms, such as increased thirst and the urge to urinate more often.
  • If it is suspected that you may be suffering from gestational diabetes, you will be invited to a screening test between 24-28 weeks gestation.
  • The screening test – an oral glucose tolerance test – involves two blood tests: one before you’ve had a high-glucose drink and one after.
  • There are several adverse effects that gestational diabetes can have on pregnancy, which include having a large baby for the gestational age (macrosomia), having too much amniotic fluid surrounding the baby (polyhydramnios), giving birth to a baby with low blood sugar (neonatal hypoglycaemia) and an increased risk of stillbirth (though this is still low).
  • The more uncontrolled your blood sugar levels are, the higher the risk of you developing complications
  • Treatment to control blood sugar levels, such as regular exercise and adopting a healthy diet, will help reduce the risks of getting gestational diabetes.
  • If you test positive for gestational diabetes, a diabetic specialist midwife will be allocated to you.
  • Remember, most women with gestational diabetes go on to have healthy babies. Speak to your doctor or midwife if you’re concerned. They’ll give you the guidance you need.