Gestational Diabetes Information


Sarah J. Buckley GP, MD

The test for Gestational Diabetes Mellitus (GDM) is still controversial. While some experts believe that GDM is a serious condition, and that every pregnant woman should be screened and treated, others believe that diagnosing and treating GDM is not only unnecessary but can cause more harm than good because labeling mother and baby with GDM can increase the risks of interventions, without clear evidence of benefit.

At present, US recommendations also vary. The American College of Obstetricians and Gynecologists (ACOG) suggests screening pregnant women either by asking about risk factors (see below) or with a blood test. Women who may be at higher risk, or whose blood test comes back positive, need a formal test for GDM, which is an Oral Glucose Tolerance Test (OGTT) (see below). In contrast, a recent large review by the US Preventive Services Task Force concluded that universal screening of all pregnant women is not justified by the current medical evidence.

Factors that make a woman more likely to have GDM include:

·       Overweight: body mass index [BMI-weight (kg)/height (m2)] greater than 25, and especially greater than 30 (obese)

·       Older than 25-years-old, and especially older than 45-years-old

·       Family members with diabetes, especially parents or siblings

·       GDM or a large baby (more than 4 kilograms/8 pounds 13 ounces and especially more than 4.5 kilograms/9 pounds 15 ounces) in a previous pregnancy

·       Member of a high-risk ethnic group, including Native American, Asian, Hispanic, and Pacific Islander.

If this list is used as above, most women will be at risk by age alone, so some suggest screening only for those who have at least one risk factor apart from age.

Screening is usually done at 24 to 28 weeks and involves drinking a high-glucose liquid (usually with the equivalent to 10 to 20 teaspoons of sugar) and testing blood sugar in the hours following. An OGTT involves fasting before the test and having more blood sampling. Note that the criteria to diagnose GDM are not standardized, which increases the controversy in this area.

High glucose levels may indicate that insulin is not working as it should to clear glucose from the blood and take it into the cells. This is normal to some extent in pregnancy, as the mother’s glucose levels need to be higher to ensure that plenty of glucose is available for her baby’s growth and function. However, a diagnosis of GDM may mean that a woman is more susceptible to diabetes even outside of pregnancy, and she needs to have another test six months later.

While it is clear that women with GDM tend to have bigger babies, we do not yet know how much this is due to the mother’s weight and weight gain, because heavier moms (and those who gain more weight in pregnancy) are more likely to have bigger babies, and are also more likely to have GDM.

We also know that children of mothers with GDM who were heavier at birth may have higher chances of diabetes, which probably relates to high levels of glucose and insulin (which acts like a growth factor) in the womb. However, it is again not clear whether this is due to the mother’s weight/weight gain or GDM and importantly, whether treating GDM makes a difference for mother or baby.

Studies have shown that when moms are diagnosed with GDM, their risk of induction and cesarean increases, both of which will mean that babies may be born before they are ready: this is especially risky for GDM babies whose lungs tend to be less mature. In some studies, there is also more risk that a baby whose mom has been diagnosed with GDM will be admitted to special care.

Overall, I believe that the best approach is to ensure that you are active, have a healthy weight, and a good diet before becoming pregnant. In pregnancy, keep active and don’t overeat, especially sweet and junk foods, and aim for even 15 to 30 minutes of light exercise three times a week, because this will benefit you and your baby and reduce the risk of GDM. Keeping your intake of sweet and starchy foods low, especially those with a high glycemic index is very important (see below). If you are diagnosed with GDM, all of these recommendations are even more important.   Personally, I would not recommend routine testing unless you have risk factors apart from age.


More information and all references in Gentle Birth, Gentle Mothering: A Doctor’s Guide to Natural Childbirth and Gentle Early Parenting Choices, Chapter 4: Your Body, Your Baby, Your Choice.
Calculate your body mass index here:
Learn about the glycemic index for foods here: