APO study used a very strict protocol for OGTT collection: blood was collected into fluoride tubes placed immediately on ice (which helped slow down the cells to stop them using glucose) and samples were processed within one hour of test completion. This is not practical in most clinical settings and is not done in WA.
We estimated the loss of glucose in OGTT samples collected into fluoride tubes and corrected glucose results had the HAPO study ice-method or fluoride-citrate (FC) Mix tubes been used. FC Mix tubes are used internationally because they stop glycolysis straight away and keep blood glucose results accurate over time, even at room-temperature. We found:
- Correction for glucose loss using the HAPO study ice-method more than doubled the rate of GDM (from 9.7% to 22.7%).
- FC tube correction gave slightly higher results compared to the HAPO study ice-method (+0.20 mmol/L) and quadrupled the rate of GDM (44.6%).
One in five women who probably had GDM but were not managed had a large baby. This is similar to the rate of women in the HAPO study who had GDM and had a large baby (16.2%, one in six).
- Correction for glucose loss using the HAPO study ice-method improved GDM prediction of risk for a large baby (from 1.1 to 1.8 relative risk compared to women without GDM).
- The higher risk for a large baby remained in women with GDM after accounting for weight, age and smoking.
- When using the FC Mix tube correction we needed to increase the GDM diagnostic criteria +0.20 mmol/L to get similar results to the HAPO study ice-method.
FC tubes are now in used in the Kimberley. We are using FC Mix tubes in Aboriginal Health Service clinics in the Kimberley that give more accurate glucose results, even if the blood sample takes a long time to reach the laboratory. We are monitoring the results of this change.
- Almost three-quarters (71.4%) of Aboriginal women with early HbA1c ≥5.6% went on to have a positive OGTT. We think these women had prediabetes going into pregnancy.
- There were clear differences between Aboriginal and non-Aboriginal women: 16.3% v 5.2% had elevated HbA1c (pre-pregnancy prediabetes) whereas 12.4% v 29.6% developed GDM during pregnancy. This suggests fewer non-Aboriginal women had prediabetes going into pregnancy compared to Aboriginal women.
- The risk of having a large baby was twice as high in women with an early HbA1c ≥5.6% compared to women with an early HbA1c <5.6% and without GDM (21.4% v 10.5%). This suggests that women with prediabetes in early pregnancy have high-risk for a large baby.
In the Kimberley all Aboriginal women have been offered an early HbA1c at their first antenatal visit since 2017. We are currently looking at outcomes for Kimberley Aboriginal women who delivered their babies between 2018 and 2021. This will give us a larger, more representative of group of Kimberley women to test the early HbA1c ≥5.6% threshold.
Current and future work:
- We will continue to lobby for Australian pathology labs to use FC Mix tubes for glucose testing – a national pre-analytical glucose working group was formed in 2020 to progress changes to laboratory practice across Australia.
- We are recruiting an additional 200 women to compare OGTT results from the new FC Mix tubes with other tests that are easier for pregnant women to do, so that less women need to do the OGTT after 20 weeks gestation.
- We are working on updating the Kimberley Diabetes in Pregnancy protocol to add the HbA1c ≥5.6% prediabetes cut-point – this will replace the early OGTT (<20 weeks gestation).
- We are planning on co-designing culturally appropriate management strategies for Aboriginal women with prediabetes in pregnancy.
- Kirke AB, Atkinson D, Moore S, Sterry K, Singleton S, Roxburgh C, Parrish K, Porter C, Marley JV. Diabetes screening in pregnancy failing women in rural Western Australia: An audit of oral glucose tolerance test completion rates. Aust J Rural Health 2019. http://dx.doi.org/10.1111/ajr.12465
- Jamieson E, Spry E, Kirke A, Atkinson D, Marley JV. Real-world gestational diabetes screening: problems with th