Poster Presentation Australasian Diabetes in Pregnancy Society Annual Scientific Meeting 2024

Shortening the pregnancy OGTT to 1 hour; how many women would be missed?  (#25)

Cecily Foged 1 , Sharon Chand 1 , Elizabeth Sterling 1 , Louise McMeeken 1 , Alexis Shub 1 , Christine Houlihan 1
  1. The Mercy Hospital for Women, Heidelberg Melbourne, VIC, Australia

Background 

The 75g Oral Glucose Tolerance Test (OGTT) is the recommended diagnostic test in Australia to detect Gestational Diabetes Mellitus (GDM), however many women find the duration of the test and the number of blood tests unpleasant. Many women undergo the test more than once in pregnancy.

We have explored the option of shortening the OGTT to 1-hour duration by reviewing the subgroup of women with GDM, diagnosed on isolated elevation of 2-hour glucose value.  

 

 

Aims 

We sought to determine: 

  1. The proportion of pregnancies which were diagnosed with GDM with 75g 2-hour OGTT, who received a positive value at the 2-hour test only.  
  1. The proportion of these women who required insulin. 
  1. The proportion of these women who experienced macrosomia, cesarean delivery or SCN/NICU admission. 

 

Method 

This is a retrospective data review of 21,850 women with a diagnosis of GDM who received antenatal care and delivered their babies at a single hospital from 2020 –2023. 

Data was collected from electronic medical records.

GDM was defined using the current ADIPS guideline.  

Results 

Table 1:  GDM diagnosis by abnormal OGTT value   

 

Total 

Total number of births 

21850 

Number of women with GDM (%) 

4716 (21.6%) 

GDM with elevated FBG (% of GDM cases) 

2252 (48%) 

GDM with normal fasting, and elevated 1 hour value * (% of GDM cases) 

1474 (31.3%) 

GDM with elevated 2-hour value only (% of GDM cases) 

654 (13.9%) 

GDM diagnosis without OGTT (HbA1c or other) 

335 

GDM with isolated elevated 2-hour glucose needing Insulin (%) 

152 (23%) 

% of total pregnancies diagnosed as GDM from 2-hour test alone 

3.0% 

* Either a positive or negative 2-hour value 

Table 2: Demographic details and perinatal outcomes in GDM with  

isolated elevated 2-hour OGTT value  

 

Total  

Number of women with GDM  

654 

Women with BMI >35kg/m2 

45 (6.9%) 

Country of birth* 

 

Australia/New Zealand/Europe/South Africa 

355 (54%) 

Aboriginal or Torres Strait Islander 

8  

Māori/ Pacific Islander 

0 

Non-white African 

21 

Middle Eastern 

26 

Asian 

134 

Indian Subcontinent 

110 

Non-Caucasian 

299 (46%) 

Cesarean delivery 

319 (47%) 

Admitted NICU/SCN 

148 (28%) 

Birth weight > 4000g LGA (centiles yet to be calculated) 

38 (5.6%) 

 

 

*Based on self-reported country of birth 

Conclusion 

GDM rates are high at this large tertiary obstetric hospital in Melbourne.   Women with isolated elevated 2-hour OGTT value represent 14% of GDM cases and 3% of the total births. Approximately one quarter of this subgroup or 0.6% of the cohort of GDM needed insulin treatment. There was a slightly lower rate of GDM in women from non-Caucasian country of birth, suggesting country of birth did not impact rate of GDM in this subgroup.  The rate of macrosomia in this subgroup was 6% and >90th centile was XX , compared to x % across the GDM population. A small number of all GDM cases currently diagnosed would be missed if a 1-hour OGTT was adopted.