Diabetes is when you have too much sugar in your blood, and it can make you sick and affect your baby’s growth. Diabetes screening is to check whether you already have diabetes or if you are at risk of developing diabetes while you are pregnant (gestational diabetes).
Diabetes screening is offered twice:
How do we screen for gestational diabetes in NZ?
At 24–28 weeks’ gestation, all women not previously diagnosed with diabetes who are at high risk of gestational diabetes should be offered the diagnostic two-hour, 75g GTT. All other low risk women should be offered screening for gestational diabetes using the one-hour, 50g oral glucose challenge test known as the polycose test.
Polycose or GTT? Pro’s and cons of each test?
Polycose test: For low risk women only. It is arguably the easiest to do. You do not need to restrict eating beforehand, can go any time of the day, is 1 blood test, 1 sweet 50g drink and you only need to wait at the lab for 1 hour.
The polycose test is highly sensitive at picking up women with GDM but it is a screening test only. The downfall is that the polycose test has a high (25%) false-positive rate. This means that up to 25% of women may get a high result, go on to have the GTT which then is negative and rules out GDM.
If the result from the polycose is ≥ 11.1 mmol/L, then we refer directly to services that specialise in diabetes in pregnancy without further testing; if the result is ≥ 7.8–11.0 mmol/L, then we arrange a GTT to diagnose (or not!) GDM.
GTT: A bit harder on pregnant people! You must fast for 12 hours before the test. This means nothing to eat from 8pm, nothing to drink except water. Then go to the lab at 8am (still nothing to eat), have a blood test, drink the 75g glucose test, wait 2 hours (still nothing to eat), and another blood test.
This is our gold standard test and is what is used to definitively diagnose GDM.
Significant risk factors that indicate it is sensible to offer 75g GTT as first option at 24-28 weeks:
BMI over 35 (increased risk of 20-27%)
Women over 40 years of age (20% risk of GDM)
Pacific, Indian and Asian women (16 - 22% risk of GDM)
Booking HbA1c 41-49
Previous baby over 4000gms
Polycystic ovary syndrome
Two 1st degree relatives with diabetes
Glycosuria (glucose showing on urine stick)
On antipsychotic medication
Declining screening: you absolutely have the right to informed choice and consent. This includes the right to decline screening for GDM. I am happy to support you if you choose to decline after reading further about GDM, risk factors, chances/risks of GDM, and the importance of healthy diet and lifestyle. Part of informed choice and consent and declining of recommendations is also to accept responsibility for your choices, health, and the outcomes of those choices (whatever they may be). My role in our partnership is to present to you information, recommendations, assess and share your risk factors with you and to document your choices. I will also revisit your choice for discussion if something changes your chances of having GDM.
If you do already have diabetes or you develop diabetes in pregnancy, you will be offered information, treatment and support, including help to eat well and stay active.
For more information about gestational diabetes click here...