That pregnancy blood glucose test

All Woman

Dear Dr Mitchell,

I just got the results back from my pregnancy glucose test and it shows that everything is normal, even though I could have sworn that my sugar levels would be high. You see, I consume a lot of sugar (I was an addict before pregnancy and am craving even more now) and thought I was at risk for diabetes, but the results show otherwise. Could the test be wrong? Is it something I should follow up on after giving birth? And what exactly does the glucose test measure in pregnancy?

The blood glucose test done in pregnancy is a screening test to determine your risk for developing gestational diabetes or detect those patients who had diabetes before the onset of the pregnancy and were not aware of this problem.

At the first visit, and throughout all visits of the pregnancy, a urine test is done to determine the presence of glucose in the urine. There is an increase in the blood flow to the kidneys during pregnancy and you could actually spill sugar in the urine even with a normal blood sugar level. The urine test is therefore not a good test for diagnosing diabetes in pregnancy and so the blood sugar test is preferred.

There are several ways of testing in pregnancy. Options include a random blood glucose which can be done irrespective of the time of the last meal; a fasting glucose; an O'Sullivan's test; and the oral glucose tolerance test. The O'Sullivan's test is done after drinking a solution containing 50 grams of glucose. There is no need to fast before the test and the blood sample is taken one hour after drinking the mixture. A value of 7.8mmol/L or greater is considered a positive test and is an indication for further testing using the glucose tolerance test which requires that you fast from 10:00 pm the night before the test, having consumed a diet with complex carbohydrates for two to three days before the test. A fasting glucose is done followed by a drink containing 75 grams of glucose. A repeat blood glucose is then done at one hour and then at two hours. If the blood glucose levels are higher then this is a confirmation that diabetes is present in the pregnancy. This will then need to be managed by an appropriate diet and possible insulin injections depending on the severity.

If you have a suspicion that you might be at significant risk for diabetes in pregnancy, then you should repeat the blood test. A blood test called glycated haemoglobin (HBA1C) can be done to give you an idea as to your glucose control over the last three months. This will also be a useful test if you are in doubt as to your glucose status.

Risk factors for diabetes mellitus includes women who are above 90kg, polycystic ovarian disease, history of having delivered a big baby of at least four kg, a bad obstetric history, including recurrent pregnancy losses and stillbirths, a past history of gestational diabetes mellitus, family history of diabetes mellitus, steroid usage, polyhydramnios (excessive fluid around the baby), excessive weight gain in the pregnancy, or being large for your dates.

A single test at the beginning of the pregnancy does not rule out diabetes mellitus and so repeat testing should be done at 24 to 28 weeks and then at 36 weeks if there are significant risk factors for developing diabetes in pregnancy.

You should reduce your risk of gestational diabetes mellitus and diabetes in your years ahead by reducing your consumption of sugar-containing foods. This is important since increased intake of sugar increases your risk for heart disease and also cancer as you get older. Refined sugar is especially bad for you, and overall a reduction in your intake of sugar is the healthy way to go.

Consult your doctor who will advise you further.

Best regards.

Dr Sharmaine Mitchell is an obstetrician and gynaecologist. Send questions via e-mail to; write to All Woman, 40-42 1/2 Beechwood Ave, Kingston 5; or fax to 876-968-2025. All responses are published. Dr Mitchell cannot provide personal responses.


The contents of this article are for informational purposes only, and must not be relied upon as an alternative to medical advice or treatment from your own doctor.




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