Poster Presentation Australasian Diabetes in Pregnancy Society Annual Scientific Meeting 2024

What is the role of HbA1c measurement in GDM pregnancies diagnosed according to ADIPS-2014 criteria? (#9)

Liam LC Clifford 1 2 , Han HS Shi 1 2 , Jeff JFK Flack 1 2 3 , Sarah SA Abdo 1 2 , Quynh QL Le 1 , Stephanie ST Terry 1 , Natasha ND Diwakar 1 , Wenjie WW Wang 1 , Cunjing CL Li 1 , Jenny JW Wright 1 , Tang TW Wong 1 2 3
  1. Endocrinology, Bankstown-Lidcombe Hospital, Bankstown, NSW, Australia
  2. University of New South Wales, Randwick, NSW, Australia
  3. University of Western Sydney, Sydney, NSW, Australia

Background:

Systematic reviews show poor sensitivity of HbA1c in identifying GDM1. However, elevated HbA1c is associated with adverse pregnancy outcomes2.

Aim:

  • To examine the distribution and sensitivity of GDM diagnosis across different thresholds of HbA1c collected at time of diagnosis.
  • To evaluate maternal characteristics and pregnancy outcomes in high versus low HbA1c groups.

 
Methods:

We examined de-identified prospectively collected demographic and outcome data from singleton ADIPS-2014 criteria diagnosed GDM pregnancies (Mar2016-Mar2024), with a sub-group of 812 pregnancies with capillary blood glucose levels (BGLs). All women were provided education on blood glucose monitoring and medical nutritional therapy. Insulin was commenced if treatment targets were not met (FBGL<5.3mmol/L, 1hrBGL<7.4mmol/L, 2hrBGL<7.0mmol/L). Metformin was not used. Sensitivity for GDM diagnosis was calculated across thresholds for HbA1c. Two groups were defined – High and Low HbA1c groups, according to patients above and below the mean HbA1c in each cohort, respectively. Pearson’s correlation coefficient (r) was calculated for HbA1c against plasma fasting, 1hr-OGTT, 2hr-OGTT, and capillary mean fasting/post-prandial BGLs. 

We compared differences in demographic and outcome findings between the groups. Outcomes assessed included insulin use, caesarean section, early delivery (<37weeks), LGA (>90th percentile), SGA (<10th percentile), neonatal hypoglycaemia (<2.6mmol/L) and neonatal jaundice (requiring phototherapy).

 

Results:

There were 2990 GDM pregnancies. Mean HbA1c was 5.2±0.4%. The sensitivities for GDM diagnosis using different HbA1c thresholds decreased with increasing HbA1c-cutoffs of 4.8%, 5.1%, 5.3% and 5.6% corresponded to sensitivities of 89%, 61%, 42% and 18%, respectively. HbA1c was more strongly correlated with fasting plasma glucose (r=0.26) and fasting capillary BGLs (r=0.29) than 1hr-OGTT (r=0.24), 2hr-OGTT (r=0.23) and mean post-prandial capillary BGLs (r=0.213), all p<0.0001. Higher HbA1c (1569/2900, 54%), defined as above HbA1c≥ 5.2% was associated with higher maternal age (32.0±5.2vs31.0±5.4,p<0.0001), gravida (3.0±1.9vs2.8±1.8, p<0.0001), parity (1.4±1.4vs1.2±1.3, p<0.0001), maternal BMI (28.6±6.5vs25.6±5.4kg/m2, p<0.0001), and total gestational weight gain (9.4±6.8vs8.6±5.3kg, p<0.001). Furthermore, higher HbA1c was associated with increasing rates of insulin therapy (57.4%vs37.6%, p<0.0001), caesarean section (40.7%vs31.3%, p<0.0001), LGA (14.7%vs10.0%, p<0.001), neonatal hypoglycaemia (12.1%vs9.2%, p<0.05), and higher insulin requirements (33.0±32.3vs22.0±18.7units, p<0.0001).

 

Conclusions:

(1) HbA1c should not be used for GDM diagnosis - as approximately 50% of women with GDM will have a HbA1c<5.2%, 

(2) HbA1c is slightly better correlated with fasting as compared to post-prandial glycaemic status. 

(3) GDM women with higher HbA1c have higher risk maternal characteristics and have higher rates of adverse pregnancy outcomes.

  1. Renz PB, Chume FC, Timm JRT, Pimentel AL, Camargo JL. Diagnostic accuracy of glycated hemoglobin for gestational diabetes mellitus: a systematic review and meta-analysis. Clin Chem Lab Med 2019;57(10):1435-49.
  2. Hughes RC, Moore MP, Gullam JE, Mohamed K, Rowan J. An early pregnancy HbA1c ≥5.9% (41 mmol/mol) is optimal for detecting diabetes and identifies women at increased risk of adverse pregnancy outcomes. Diabetes Care. 2014 Nov;37(11):2953-9. doi: 10.2337/dc14-1312. Epub 2014 Sep 4. PMID: 25190675.