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Gestational diabetes screening, examinations and tests

Gestational diabetes (GDM) is a condition resulting in high blood sugar (glucose) levels that is first found during pregnancy.

Gestational diabetes occurs in around 1 in 25 pregnancies in the UK.

Almost all women have some degree of impaired glucose tolerance as a result of hormonal changes that occur during pregnancy. That means that their blood sugar may be higher than normal, but not high enough to have diabetes.

Usually the mother's pancreas is able to produce more insulin (about three times the normal amount) to overcome the effect of the pregnancy hormones on blood sugar levels. If, however, the pancreas cannot produce enough insulin to overcome the effect of the increased hormones during pregnancy, blood sugar levels will rise, resulting in gestational diabetes.

Diabetes in pregnancy that is not well managed can causes complications, including an increased risk of a miscarriage and stillbirth.

Gestational diabetes risk factors

You may be at increased risk of developing gestational diabetes if:

  • Your body mass index ( BMI) is over 30
  • You've had a baby previously weighing 4.5kg (10lbs) or more at birth
  • You had gestational diabetes in an earlier pregnancy
  • You have a close family history of diabetes
  • You have South Asian, black Caribbean, or Middle Eastern family origins

Gestational diabetes screening

The NHS recommends every pregnant woman with one or more risk factors should be offered a screening test for gestational diabetes.

Depending on your risk factors, you may be screened for gestational diabetes at varying stages of your pregnancy. Early in pregnancy a blood test measuring blood glucose will be performed and an oral glucose tolerance test (OGTT) may also be recommended. Later in pregnancy an oral glucose tolerance test is performed.

What is the oral glucose tolerance test for gestational diabetes?

For an oral glucose tolerance test, a sample of your blood will be tested – before you have had breakfast. You will then be given a sweet glucose drink. Two hours later another blood tests is performed to determine how well your body deals with the glucose.

Gestational diabetes test results

If the tests done earlier in pregnancy show you do not have gestational diabetes, you may still be asked to have another test at around weeks 24-28.

If you are diagnosed with gestational diabetes, you will be given advice about how to manage the condition and how to monitor your blood glucose levels yourself at home.

Monitoring your growing baby

Because gestational diabetes in the mum increases the baby's risk of risk of complications, additional monitoring may be arranged.

Babies of mums with gestational diabetes can be larger than normal when they are born.

Appointments may include:

  • Around weeks 18-20 of the pregnancy, an ultrasound scan may be carried out to check the baby for any heart abnormalities.
  • Around weeks 28, 32, 36 and regularly beyond this, ultrasound scans will be carried out to check the baby's growth and the amount of amniotic fluid surrounding the baby in the womb.

Depending on the results of these checks, additional precautions may be factored into your birth plan.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on December 23, 2015

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