By Professor Fidelma Dunne

Gestational Diabetes (GDM) is a form of diabetes that begins during pregnancy. It usually starts after about 20 weeks of pregnancy and affects about 12% of women, with the numbers increasing alongside obesity levels.

GDM usually occurs because the body cannot produce enough insulin to meet the extra needs required in pregnancy although in some cases the condition may have existed before pregnancy.
Of the women who develop GDM during pregnancy, about 70% can control their blood sugar by making changes to their diet and increasing their exercise. About 30% of women with GDM will require insulin. If you require insulin treatment, the dose of insulin may increase as your pregnancy progresses, and insulin adjustments will be made frequently, in conjunction with your diabetes team, to maintain your blood glucose strictly within target.

  • Are you at risk factors for developing gestational diabetes during pregnancy?
  • Are you over 30 years of age?
  • Are you overweight or obese?
  • Do you have Polycystic Ovarian Syndrome (PCOS)?
  • Are you carrying multiple babies (twins/triplets)?
  • Do you have a family history of diabetes?
  • Are you of non-Caucasian ethnicity?
  • Do you have a history of miscarriages, stillbirth, neonatal death or a baby born with a congenital abnormality?
  • Have you previously had gestational diabetes?
  • Have you previously delivered a large baby (over 4kg)?

What are the symptoms?

For many women, gestational diabetes may cause no symptoms. Some women however may experience symptoms such as increased thirst, increased need to pass water or increased hunger, although these are also common later in pregnancy anyway.

If you are at risk for GDM you will be diagnosed using an ‘oral glucose tolerance test’.
An oral glucose tolerance test (OGTT) is a simple screening test for gestational diabetes, carried out around weeks 24 to 28 of your pregnancy.
You will be asked to fast from the night before your test.

When you attend the clinic for your test a blood sample will be taken from your arm.
You will then be given a sugary drink (Polycal) plus a further quantity of water, both of which are measured amounts so you will need to drink it all.

You will then need to rest for an hour after which another blood sample will be taken.

The final blood test will be taken one hour later. You will then be free to eat and go home.

The three blood samples will be sent to the Laboratory for analysis to see how your body deals with the glucose.


Controlling your weight gain during pregnancy is very important. Healthy eating and staying active during pregnancy are two of the most important ways to control blood sugar and treat gestational diabetes.
It’s very important to discuss your diet and exercise plan with your healthcare provider.
Remember: if you do develop gestational diabetes, it can be controlled.

After pregnancy GDM goes away in about 80% of women, the other 20% of women will continue to have diabetes or pre diabetes.


Fidelma Dunne holds a Personal Professorship in Medicine and is a Consultant Endocrinologist at Galway University Hospitals. Her major research interest is in the area of pregnancy and diabetes.