Antenatal screening for diabetes in pregnancy
Read our guide below to understand what to expect from antenatal screening for gestational diabetes.
You can also download a PDF version of this patient information by following the link on the right.
What is gestational diabetes?
It’s a form of diabetes which affects an estimated 5% (5 in 100) of pregnant women.
There’s no known specific cause, but it’s believed the hormones of pregnancy may block the action of insulin in the pancreas resulting in high blood sugars.
High blood sugar levels in the mother’s body pass through the placenta to the developing baby. The increased levels can be associated with an increased rate of complications in the baby. This includes:
- large size at birth
- birth trauma
- hypoglycemia (low blood sugar) for the baby
- jaundice.
Maintaining control of blood sugar levels significantly reduces the risk to the baby. If you have gestational diabetes, doctors and midwives will look after you. They’ll teach you how to monitor your blood glucose levels and closely monitor the growth of your baby.
When does gestational diabetes start?
Usually in the second half of pregnancy but it goes away after the baby’s born. Occasionally, we find gestational diabetes in the first months of pregnancy which could suggest diabetes existed before you were pregnant.
How we test for gestational diabetes
When you first see your midwife for the booking visit, they’ll take various blood tests. One of these is to test for diabetes in pregnancy with a random blood glucose (RBG) (sugar test).
A normal result is below 7.0mmols. If your test is normal no further tests are needed.
If the result is raised, we recommend a further test called a glucose tolerance test (GTT).
At 28 weeks of pregnancy
We recommend that women considered to be at a slightly increased risk of having gestational diabetes (diabetes of pregnancy) have a glucose tolerance test. Your midwife will discuss this with you at your first booking appointment.
Women who are at risk includes those who have:
- had a previous baby weighing over 4.5kg
- a family history of diabetes or gestational diabetes (parent or sibling only)
- a family origin of South Asia, black Caribbean or Middle Eastern
- a body mass index over 30 (this is a ratio of your weight and height calculated by your midwife at booking)
- polycystic ovarian syndrome
- had a stillbirth or unexplained pregnancy loss after 28 weeks of pregnancy
- any specific factors arising during pregnancy, for example, glucose++ in your urine on one occasion, or glucose+ on two occasions or an increase of fluid around the baby (polyhydramnios).
What happens in a glucose tolerance test?
A GTT is a test where we challenge your body with a measured dose of sugar.
You’ll need to have nothing to eat or drink for 12 hours before the test is taken including chewing gum.
You can have sips of water.
No smoking (before the test). Talk to your midwife if you need help with stopping smoking.
What happens at your GTT?
We’ll take an initial blood test and give you a glucose drink.
After this, we’ll ask you to stay in the hospital clinic for the next two hours to sit and rest. Please bring a book/magazine to read.
Two hours after the glucose drink, we’ll take another blood test. You can then leave and carry on as normal. We’ll contact you if the result is positive and refer you to the diabetes specialist midwife.
You may wish to bring a healthy snack to eat following your GTT test.
How to arrange a GTT
Your community midwife or hospital doctor will arrange the GTT for you.
These tests are in high demand. If you can’t attend call the clinic that booked your appointment to rearrange.
GTT results
If your results are above the expected normal levels for pregnancy, we treat you as having gestational diabetes (diabetes of pregnancy). Or if your post prandial reading is low this, would also indicate a GDM diagnosis.
We’ll refer you to a diabetes specialist midwife for care and advice. You’ll also be seen in the antenatal clinic.
If you don’t hear anything within a week after your test, your result will be negative but please ask your community midwife to check your results on your next routine appointment.
Contact us
Stoke Mandeville Hospital Antenatal Clinic
01296 316227 (daily at 9am)
Wycombe Hospital Antenatal clinic
01494 425575
Diabetes specialist midwife
01296 255790