Written by:

Miss Tara Hughes


Miss Hughes is an Obstetrics and Gynaecology registrar working in the North West London 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. She is now lead clinician at My BabyManual, working with healthcare specialists and mothers to produce relevant and informative patient-centred content. Her specialist interests include fertility and minimal access surgery. She is also expecting her first baby in December 2020!

Understanding Gestational Diabetes?

In this article:

  • What is gestational diabetes?
  • Who gets gestational diabetes?
  • Symptoms
  • Testing for gestational diabetes
  • Effect on pregnancy
  • How problems may develop
  • Antenatal care for gestational diabetes
  • Treatment
  • Gestational diabetes in labour
  • Care following delivery
  • Long-term effects
  • Main Points

Understanding Gestational Diabetes?

What is gestational diabetes?

Gestational diabetes mellitus (GDM) is a type of diabetes that only happens in pregnancy and usually goes away once the baby is born.

Normally blood sugar (glucose) levels are kept within a strict range by the hormone insulin. Glucose is able to cross the placenta and enter the baby’s bloodstream. In pregnancy, the body cleverly adapts to develop some resistance to the effects of insulin, therefore allowing more glucose to be available to the baby. The mum’s blood glucose levels will remain normal as more insulin is produced to compensate. If the resistance to insulin becomes too high and the mum cannot compensate, then GDM develops. This results in the mother’s blood sugar levels being high.

Who gets gestational diabetes?

Diabetes is the most common medical condition in pregnancy, affecting 2-5% of pregnancies – the majority of these women will have GDM and a small minority will have pre-existing type 1 or type 2 diabetes. Although any pregnant woman is at risk of developing diabetes, anything that increases your risk of resistance to insulin increases the risk of developing GDM. Risk factors include:

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

GDM is more common in the second half of your pregnancy, though rarely it can occur earlier. The condition is also becoming more common as levels of obesity in the population rise and women delay pregnancy until later in life.


Most women with gestational diabetes will not be aware they have it. This is why it is important that if you are asked, you attend the test for gestational diabetes. If your blood 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

Women are “screened” at the first appointment with the midwife to identify if they have any of the risk factors above and are therefore at higher risk of developing GDM. These women are invited to have an “oral glucose tolerance test” or OGTT at 24-28 weeks or earlier if they have had GDM in a previous pregnancy. Some hospitals invite all pregnant women to have on OGTT as most of the patients at the unit are considered “high risk”.

Women are given a drink containing 75g of glucose to see how well the body is able to process that sugar. In women who have high insulin resistance due to GDM, the sugar is not processed very well and the woman’s sugar level remains high 1-2 hours after the drink.

If you are not invited to an OGTT as a result of 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:

How problems may develop

When sugar levels are continuously high, the baby is exposed to more sugar resulting in abnormally large growth and higher fat deposits. The baby also takes in more amniotic fluid and produces more urine, resulting in excess amniotic fluid or polyhydramnios. The excess fluid puts the pregnancy at risk of preterm delivery and cord prolapse. Some doctors may recommend induction of labour at 39-40 weeks if the baby is large and you have GDM to avoid the baby getting larger. If the baby is 4kg or more at delivery, and particularly 4.5kg or more, it may struggle to descend into the birth canal during labour, resulting in failure to progress or obstructed labour. Women in this situation will need a caesarean section in labour.

In vaginal deliveries, larger babies may require an assisted delivery, i.e. a suction cup (ventouse) or forceps. Larger babies have wider shoulders so are at greater risk of shoulder dystocia — where the shoulders are stuck after delivery of the head; this may result in greater risk of injury to the baby as well as increased risk of tears for the mother. Finally, because the womb has been holding a large baby, it takes longer for it to clamp down after delivery which is the natural way to stop bleeding. Mums are therefore at higher risk of bleeding following delivery of a large baby, but this can be managed with medication.

Antenatal care for gestational diabetes

If you have been diagnosed with gestational diabetes, you will usually be seen every 1-2 weeks in a joint antenatal and diabetes clinic. You will have all of the regular antenatal care in addition to the diabetic care. The diabetes team will show you how to test your blood sugar at home using a finger prick machine (capillary blood glucose monitoring) and how to record it in a book. Some hospitals now have apps for you to record your readings. Your glucose levels will be checked at the appointments and treatment adjusted as necessary.

You are also likely to have one to three extra scans to check the baby’s size and the amniotic fluid level. These scans may happen between 28-36 weeks and are usually 4 weeks apart.

From 34 weeks onwards, your team will discuss your delivery plan with you. Most women can have a normal delivery and are not recommended to have an induction of labour until 40+6 weeks. If your sugars are poorly controlled, you are requiring more and more medication to get it under control or the baby is large, induction of labour will be recommended before your due date.


As all of the negative consequences of GDM are a direct result of the glucose level, 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.

Gestational diabetes in labour

When it comes to delivering your baby, you will need to be in a labour ward so that there are obstetricians on standby in case you experience any of the complications discussed above. The labour process itself, as well as pain relief options, are the same as for a non-diabetic pregnant woman. The only additional monitoring required is hourly blood glucose readings and you may need insulin via an intravenous infusion or drip (“sliding scale”) if the glucose level is high. The baby’s heartbeat will be monitored on an electric trace or “CTG” like all women on the labour ward. Again, most women with GDM will have an uncomplicated labour and delivery without intervention from an obstetrician.

Care following delivery

After delivery, any medication for gestational diabetes is stopped. We will check both your and your baby’s blood sugar levels periodically in the first 24 hours. Your baby will stay with you (unless there was any complication with delivery) and it is recommended that you feed the baby as soon as possible after birth and then every two to three hours. This is because babies born to diabetic mothers are more likely to experience low blood sugar levels. If the baby’s sugar level is low despite feeding it may need additional feeding via a tube directly into the stomach or a dextrose infusion via a drip. If mum and baby’s blood sugar levels are well controlled in the first 24 hours, then you can be discharged to community care pending the normal postnatal checks.

Long-term effects

Unfortunately, gestational diabetes puts you at risk of developing type 2 diabetes outside of pregnancy. Up to 50% of women who had GDM will develop type 2 diabetes within 5 years of delivering their baby. Your GP will do a fasting blood sugar at your 6-week postnatal check and should check you for diabetes annually. 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 check every year, even if you feel well.

Children of a mother who develops GDM are also at increased risk of both obesity and diabetes in later life. To reduce the risk of getting diabetes, both for your children and yourself, it is important to maintain a healthy weight and continue with regular exercise and a healthy diet.

Main Points

  • Gestational diabetes occurs when pregnant women become very resistant to the hormone insulin resulting in high blood sugar (glucose).
  • Gestational diabetes is a common condition affecting 2-5% of pregnancies
  • You are at more risk of developing GDM if you are overweight, you have previously had GDM or a baby >4kg, diabetes runs in your family or if you are of a certain ethnic group.
  • High-risk women will have an oral glucose tolerance test between 24-28 weeks
  • There are several adverse effects that gestational diabetes can have on pregnancy, which include having a large for gestational age baby(macrosomia), having too much amniotic fluid surrounding the baby (polyhydramnios) and increased labour interventions such as induction, instrumental delivery and caesarean section
  • The more uncontrolled your blood sugar levels are, the higher the risk of you developing complications
  • You will be seen every 1-2 weeks by a diabetic team and will have at least 1 extra scan between 28 and 36 weeks
  • Treatment to control blood sugar level can be achieved by regular exercise and adopting a healthy diet but may require tablets (metformin) or injections (insulin)