Gestational Diabetes Screening

Diabetes of pregnancy, or gestational diabetes (GD) occurs in women predisposed towards diabetes, when the placenta secretes hormones that increase resistance to insulin. Women generally cannot control whether or not they will develop gestational diabetes, but, once gestational diabetes is diagnosed, diet and exercise are very important in its management. Some affected women will also require treatment with insulin injections. Untreated GD can lead to multiple pregnancy complications, the most notable being fetal macrosomia. This is when the baby grows too large. It can cause difficulties with delivery, in addition to other concerns.

The check for gestational diabetes generally takes place between weeks 24 and 28, but women at higher risk may have an initial screen done earlier, in the first trimester.

Checking for GD at 24-28 weeks is done with an oral glucose tolerance test (GTT), where blood sugar levels are tested after the administration of a sweet drink. The OB will recommend one of two approaches.

The 1-Step Diagnostic approach involves a 2-hour test. Women fast for at least 8 hours (water is permitted) and are given a sweet drink (75g). Their blood sugar is tested before the drink, after one hour, and after two hours. If any of these blood sugar levels is above cut-off, GD is diagnosed, and a referral is made to the diabetes clinic for management. Women will be given advice regarding diet and exercise and will be provided with a glucose meter to monitor their blood sugars. They will report back to the clinic regularly, and insulin will be prescribed to women who cannot adequately control their blood sugar levels with lifestyle modification alone.

In the Screening and Diagnostic 2-Step approach, women are given a sweet drink (50g) and their blood sugar is tested one hour later. Fasting is not required. If the blood sugar is above cut-off, they must then do the 2-hour diagnostic test described above.