Poster Presentation International Association of the Diabetes and Pregnancy Study Groups 2022 - Hosted by ADIPS

Comparison of insulin requirements in women diagnosed with gestational diabetes on oral glucose tolerance test. (#97)

Reetu Gogna 1 , Vanessa Heron 2 3 , Lik-Hui (William) Lau 1 , Suet-Wan Choy 1 2 4
  1. Department of Obstetrics and Gynaecology, Mercy Hospital for Women, Heidelberg, Melbourne, VIC, Australia
  2. Department of Nephrology and General Medicine, Austin Health, Heidelberg, Melbourne, VIC, Australia
  3. University of Melbourne, Parkville, Melbourne, VIC, Australia
  4. Department of Renal and Obstetric Medicine, Eastern Health, Box Hill, Melbourne, VIC, Australia

Introduction

Gestational diabetes mellitus (GDM) affects 16% of Australian pregnancies.1 In Australia, women are routinely screened for GDM with a 75g oral glucose tolerance test (OGTT) at 26-28 weeks’ gestation, or earlier if high risk.2 Using the Hyperglycaemia and Adverse Pregnancy Outcomes criteria, GDM is diagnosed if blood glucose levels (BGLs) are elevated during OGTT (fasting ≥5.1mmol/L; 1-hour ≥10mmol/L; 2-hour ≥8.5mmol/L).3

Women are required to monitor BGLs fasting and 2-hours post-prandially, but not 1-hour post-prandially. Treatment targets remain controversial,2 with our centre utilising BGL targets of <5.5mmol/L for fasting and <6.5mmol/L 2-hours post-prandially. If dietary and lifestyle modification fails to achieve targets, pharmacotherapy is required.

Presently, it is unclear whether the time points at which BGLs are elevated on an OGTT influence treatment outcomes. In particular, the frequency of insulin use in women diagnosed on an elevated 1-hour BGL is unknown, given monitoring is not undertaken 1-hour post-prandially. This study aims to determine whether there are differences in insulin requirements based on OGTT results.

Method

A single-centre retrospective study was conducted on women diagnosed with GDM on OGTT during 2020. Patients were identified from a database maintained by diabetes nurse educators. Electronic medical records were used to collect demographic data, mode of delivery, gestational age at delivery, and neonatal birthweights.

Results

GDM was diagnosed in n=873 patients; median age 33 years (IQR 30,36); median BMI 27 kg/m2 (IQR 23.5,30.5); n=276 primigravida; n=858 singleton and n=15 twin pregnancies; early OGTT in n=209 and routine OGTT in n=664.

Diagnosis was established by the following elevated results: Fasting only (n=204), 1-hour only (n=177), 2-hour only (n=140), Fasting and 1-hour (n=91), Fasting and 2-hour (n=19), 1 and 2-hour (n=145) and Fasting, 1 and 2-hour (n=97).  

Frequencies of insulin requirement in these groups were: Fasting (n=88/204, 43%); 1-hour (n=40/177, 23%); 2-hour (n=32/139, 23%); Fasting and 1-hour (n=47/91, 52%); Fasting and 2-hour (n=7/19, 37%); 1 and 2-hour (n=50/145, 34%) and fasting, 1 and 2-hour (n=57/97, 59%). Metformin was used in n=2 patients.

The median gestational age at delivery was 38 weeks (IQR 37,39). Deliveries occurred via normal vaginal delivery (n=377), instrumental delivery (n=105), caesarean section (n=386), unknown (n=5).

Conclusion

Being diagnosed with GDM solely on an elevated 1-hour result on an OGTT conferred the lowest risk of insulin treatment, however, almost a quarter still required insulin. Conversely, women diagnosed with GDM based on elevated readings throughout the OGTT were at highest risk of requiring insulin.

  1. Australian Institute of Health and Welfare. Incidence of gestational diabetes in Australia. 2019.
  2. Nankervis A MH, Moses R, Ross GP, Callaway L, Porter C, Jeffries W, Boorman C, De Vries B, McElduff A,. ADIPS Consensus Guidelines for the Testing and Diagnosis of Gestational Diabetes Mellitus in Australia and New Zealand. 2014:1-8.
  3. Metzger B, Lowe LP, Dyer AE, et al, HAPO Study Cooperative Research Group. Hyperglycemia and adverse pregnancy outcomes. N Engl J Med. May 8 2008;358(19):1991-2002. doi:10.1056/NEJMoa0707943