Pregnancy and the Glucose Tolerance Tests (GTT)

by - November 06, 2023

The glucose tolerance test (GTT) is a stress test on your body to see if your insulin is managing your blood glucose levels well when you consume 75g of glucose syrup on an empty stomach. All pregnant women are offered the GTT around Week 27-29 when the placenta produces more of the hormones that cause insulin resistance. High risk women like me who have a family history of Type 2 Diabetes and Chinese-Vietnamese descent are given the GTT around Week 14-16 once the placenta has formed. From what I've gathered, women who had gestational diabetes are given the GTT in Trimester 1.

If you're going for a GTT, make sure you follow the preparation guidelines carefully so you don't accidentally skew the results and get misdiagnosed. Your pathology lab should give you an info sheet specific to their testing requirements, but here is a general guide if you want to learn more:

The irony is I was working in a product team building a pathology booking system when I got pregnant. Pregnant women are treated like pin cushions we are sent for so many blood tests in Trimester 1. I went from researching what pathology patients need to being a regular pathology patient.

The GTT is a 2 hour+ test. When you arrive, usually first thing in the morning as you need to fast for 8-12 hours. If you fast for longer, your body may do a glucose dump and cause you to fail the fasting blood glucose level test and be diagnosed with diabetes, pre-diabetes or gestational diabetes depending on why your doctor sent you for the test and your medical condition.

Some people abhor the test and feel sick from the glucose syrup. I was thankfully not one of these people. After my fasting blood vial was taken, I sipped my 75g of glucose in a 10 minute window without issue. The pathology collector set a timer for 1 hour from my fasting test and at the one hour mark, another blood vial was taken. Another 1 hour timer was set and at the 2-hour mark from drinking the syrup, my third blood vial was taken and after checking I was feeling OK, they sent me on my merry way with cotton balls taped to both arm nooks. They rotate arms for the GTT so one arm gets pricked twice at the fasting and 2 hour mark, and one arm gets pricked once at the 1 hour mark.

I failed my GTT at 16 weeks pregnant, and have been diagnosed with gestational diabetes due to my 1 hour test results based on the diagnostic criteria below, as I had a 10.7mmol/L result. My fasting and 2 hour results were fine.

International Association of the Diabetes and Pregnancy Study (IADPSG)

  • 0 h ≥ 5.1 mmol/L
  • 1 h ≥ 10.0 mmol/L
  • 2 h ≥  8.5 mmol/L

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