Gestational diabetes in Singapore: the glucose tolerance test, your results and blood sugar targets

Gestational diabetes (GDM) is high blood sugar that shows up for the first time in pregnancy. In Singapore it affects about one in five pregnant women, and every mum-to-be is offered a 75g oral glucose tolerance test (OGTT) between 24 and 28 weeks. You're diagnosed if any one of three readings reaches the cut-off: 5.1 mmol/L fasting, 10.0 one hour after the sugar drink, or 8.5 two hours after. Most women bring it under control with food and activity, it usually clears by six weeks after birth, and you'll need a repeat test 6 to 12 weeks after delivery. Below are the test steps, how to prepare, what your numbers mean and the targets KKH, NUH and HealthHub give for home testing.

What gestational diabetes is

Your placenta makes hormones that push your blood sugar up and make your body resist insulin, the hormone that moves sugar out of your blood. Most women make enough extra insulin to cope. When your body can't keep up, sugar builds up in your blood and you have GDM. It usually starts in the second or third trimester and goes away after delivery.

It's common here. NUH and HealthHub put it at one in five pregnant women in Singapore, and KKH says it can affect nearly a quarter. It rarely causes symptoms, which is why everyone is screened instead of waiting for signs. Very high levels can make you thirsty, pass urine more often or lose weight. It isn't your fault: HealthHub notes that eating well and exercising lowers the risk but can't remove it.

Well controlled, most women with GDM have healthy pregnancies and healthy babies. Poorly controlled, it raises the chance of a bigger-than-average baby (and a harder delivery), low blood sugar or jaundice in your newborn, high blood pressure in pregnancy, induction or caesarean, and diabetes for you later in life.

Who is tested earlier

If you're at higher risk, your doctor may offer the OGTT in the first trimester. HealthHub says this early test is usually a 2-point OGTT. If it's normal, you're tested again at 24 to 28 weeks with the full 3-point test. Singapore's hospitals list these risk factors:

• A body mass index (BMI) of 23 or more before pregnancy (KKH and HealthHub; NUH's list says above 25)
• A parent or sibling with diabetes
• GDM in a previous pregnancy
• A previous baby who weighed more than 4kg at birth
• Being 40 or older
• High blood pressure, polycystic ovary syndrome or a past stillbirth
• Glucose in your urine at a check-up, or known prediabetes

Gaining a lot of weight during pregnancy also raises your risk. If you have none of these, you can still get GDM, so the standard test at 24 to 28 weeks is still worth doing. Our 24 weeks pregnant guide shows where it sits among your other checks.

The glucose tolerance test, step by step

The OGTT is a morning blood test with a sweet drink in the middle. Plan for the whole visit to take 2 to 3 hours. This is how KKH, NUH and HealthHub describe it:

1. Fast the night before. NUH asks you to stop eating from midnight; HealthHub says nothing but a little plain water for 8 to 10 hours before the test.
2. At the clinic, a nurse takes your first blood sample, the fasting reading.
3. You drink a 75g glucose solution and finish it within 5 minutes.
4. A second blood sample is taken one hour after the drink.
5. A third is taken two hours after the drink. Then you can eat.

Between the blood draws you sit and wait. Walking around, eating or smoking changes the result, so bring a book, a charged phone or some work, and a snack for afterwards.

How to prepare

• Eat your normal balanced meals in the days before. HealthHub warns that dieting, or a run of heavy meals, makes the result less reliable.
• Skip hard exercise before and during the test, because it changes your blood sugar.
• Have nothing but a small amount of water for 8 to 10 hours before.
• Don't eat, drink or smoke during the test.
• Tell your doctor beforehand if you take regular medication or have had weight loss surgery.

Side effects

The test is safe for you and your baby. The drink is very sweet and can make you feel sick or dizzy, and rarely it makes you vomit. Tell the nurse if you feel unwell. If you vomit, KKH says the test is rescheduled for another day. You can decline the test, and KKH says that choice won't affect the rest of your antenatal care, though it strongly encourages it.

What your results mean

You have GDM if any one of the three readings is at or above these levels. HealthHub publishes these plasma glucose cut-offs, which come from the Agency for Care Effectiveness guide:

One high reading is enough. HealthHub adds that your doctor confirms the diagnosis after looking at your pregnancy as a whole. Ask for your three numbers so you can see which one was high and by how much.

After a diagnosis you join a small team. At KKH it's obstetricians, endocrinologists (diabetes doctors), specialised nurses and dietitians. NUHS arranges an education session, a nurse teaches you to prick your finger and read a glucometer, and a dietitian builds an eating plan with you. If you're still choosing a doctor, our guide to choosing a gynae compares the public hospital clinics.

Blood sugar targets for home testing

You'll test your own blood sugar at home. NUH asks for at least two days a week, seven times on each of those days: before and two hours after breakfast, lunch and dinner, and at bedtime. HealthHub says to time the after-meal reading from your first mouthful. Your doctor may ask for more if your readings are high or you start insulin.

These are general ranges, and your doctor may set different ones for you. If you're not on any diabetes medicine, a reading slightly below the range while you feel well isn't a concern, HealthHub says. Write every reading down, with a note when a meal was unusual or you were ill, and bring the log to each visit. Your doctor uses it to decide whether food changes are enough or you need medicine.

How it's treated

Most women manage with food and activity alone. A dietitian helps you build balanced meals at regular times and right-size your portions. HealthHub suggests My Healthy Plate: half your plate fruit and vegetables, a quarter wholegrains and a quarter protein, with 2 to 4 hours between meals and snacks. Our gestational diabetes diet guide turns that into hawker and home meals, and our guide to eating well in pregnancy covers nutrition beyond blood sugar.

Activity helps your body use insulin. NUHS and HealthHub aim for at least 150 minutes of moderate activity a week, such as brisk walking or swimming, once your doctor agrees. A short walk after meals is an easy start, and our guide to safe exercise during pregnancy covers what to avoid.

If your readings stay high, or a scan shows your baby growing larger than expected, you'll need medicine. NUH says it's usually injected insulin; HealthHub also lists oral medicine such as metformin. Needing it says nothing about your effort, because GDM can get worse as pregnancy goes on.

Expect more visits too. KKH checks your HbA1c (a three-month average of your blood sugar) and your blood pressure and urine at every visit, because GDM raises the risk of pre-eclampsia, and may scan your baby's growth more often. Our prenatal checkups and scans guide shows the usual schedule.

Labour and birth

Many women with well controlled GDM have a normal birth. Your team talks to you about the timing and type of delivery based on your blood sugar control, your baby's size and your blood pressure. HealthHub says induction is considered at term, typically 38 to 39 weeks, if you're on medicine, your baby is expected to be large or your sugar isn't well controlled.

In labour your blood sugar is checked often, and some women get insulin through a drip. After birth, your baby's blood sugar is tested because it can dip, and it's treated if it's low. Breastfeeding is encouraged.

After your baby is born

Most women can stop their GDM medicine after delivery, and HealthHub says GDM usually goes by six weeks after birth. The follow-up test is the part that gets missed in the newborn weeks, so book it early.

• Repeat OGTT at 6 to 12 weeks after delivery. HealthHub says this one is a 2-point test. If you deliver at NUH, the O&G team arranges it and the NUH Diabetes Clinic invites you back within six months to go through the result.
• If the result is abnormal, KKH refers you to a diabetes doctor or the polyclinic.
• If it's normal, keep screening. HealthHub and NUH say every one to three years; KKH says every year, because you still have a one in three chance of diabetes later.
• HealthHub says women here who had GDM are 12 times more likely to develop type 2 diabetes within five years of delivery than women who didn't.
• Tell your doctor about your GDM when you plan another pregnancy, as it can come back.

To lower your risk, breastfeed if you can, stay active and keep to a healthy weight. If your BMI is above the healthy range, NUHS suggests losing about 7% of your body weight over six months. Our pregnancy weight gain calculator shows the range to aim for while you're pregnant.

Frequently asked questions

How long does the glucose tolerance test take?

Plan for 2 to 3 hours. The blood draws are at the start, one hour and two hours after the drink, and you sit and wait in between. Go early in the morning, since you've been fasting overnight.

Can I drink water before the OGTT?

Yes, a small amount of plain water. KKH and NUHS allow water during the fast. Skip coffee, tea, juice and every other drink until the test is done.

Is a fasting reading of 5.1 gestational diabetes?

A fasting reading of 5.1 mmol/L or higher meets the cut-off HealthHub publishes, and one high reading out of three is enough for a diagnosis. Your doctor confirms it after looking at your whole pregnancy.

What happens if I vomit during the test?

Tell the nurse. The result won't be accurate, so KKH reschedules the test for another day.

Will I need insulin?

Not necessarily. Most women control GDM with food and activity. You'll need medicine, usually insulin and sometimes metformin, if your readings stay above target or your baby is growing large.

Does gestational diabetes go away after birth?

Usually, within about six weeks. You still need the repeat OGTT at 6 to 12 weeks, and regular diabetes checks after that, because GDM raises your risk of type 2 diabetes.