28th March 2026, A/Prof Chee L Khoo
Not all women with gestational diabetes mellitus (GDM) are the same. There are three subtypes of GDM – isolated fasting hyperglycaemia, isolated post prandial hyperglycaemia or combination of both being abnormal. Similarly, not all women with GDM end up the same after delivery. Women with GDM are recommended to have an OGTT at the 6 weeks postpartum. It would be ideal if 100% of women get to the post-partum testing but for various patient, doctor and system issues, the number is sadly less than 50%. Different GDM subtypes may have different postpartum glycaemic tolerance and knowing which subtypes have a higher likelihood of ongoing glucose dysmetabolism may allow us to prioritise our monitoring.
Van, Julie et al looked a cohort of women diagnosed with GDM from the Study of Women, Infant Feeding, and Type 2 Diabetes Mellitus After GD Pregnancy (SWIFT), who were recruited within the Kaiser Permanente Northern California integrated health care system between 2008 and 2011 (1).
Women who delivered before 35 weeks and women who had T2D diagnosed at 6-9 weeks post-partum were excluded from the study. This was to exclude women with pre-existing diabetes before pregnancy.
GDM subtypes
GDM was diagnosed in accordance with Carpenter and Coustan criteria using the antepartum 3-hour, 100-g OGTT, with at least 2 elevated glucose measurements ≥ 5.2 mmol/L at fasting and ≥ 10.0 mmol/L at 1-hour, ≥ 8.6 mmol/L at 2-hour, and/or ≥ 7.8 mmol/L at 3-hour post-load time points (2). See Table 1
| Table 1. Carpenter and Coustan criteria: ≥ 2 abnormal | |
| Glucose reading (mmol/L) | |
| 0 hour | ≥5.2 |
| 1 hour | ≥ 10.0 |
| 2 hour | ≥ 8.6 |
| 3 hour | ≥ 7.8 |
GDM subtypes were based on the dominant metabolic defect of the diagnostic OGTT: (1) isolated post-load glucose intolerance defects (GD-P) based on elevated measurements at least 2 post-load time points only; (2) fasting hyperglycaemia defects (GD-F) based on elevated measurements at fasting and any 1 postload time point; and (3) mixed defects (GD-M), with elevated measurements at fasting and at least two 2 post-load measurements.
368 women (36.6%) were Asian, 78 (7.8%) were Black, 308 (30.6%) were Hispanic, 235 (23.4%) were White, and 16 (1.6%) were multiracial.
Baseline characteristics of the women with GDM
1005 women with a median age of 33.2 years, 403 (40.1%) of whom had obesity before pregnancy were studied.
The GDM subtypes amongst the participants were:
- GD-P: 61.3%
- GD-F: 12.3%
- GD-M: 26.4%
The breakdown amongst Asian women were slightly different:
- GD-P: 67.4 %
- GD-F: 9.5 %
- GD-M: 23.1 %
The breakdown amongst Black women were very different:
- GD-P: 50.0 %
- GD-F: 9.0 %
- GD-M: 41.0 %
Women with the GD-P subtype had lower pre-pregnancy BMIs than those with GD-F and especially GD-M. GD-P was the only subtype for which the majority of women did not have obesity (29.4% obese vs 54.0% obese for GD-F and 58.5% for GD-M.
Despite differences in pre-pregnancy BMI, women had similar gestational weight gain across subtypes. However, the GD-P subtype had the lowest proportion of women who gained weight above guidelines 28.9% vs 40.3% for GD-F and 42.3% in GD-P (p = .001).
Women with GD-P participated in less moderate-to-vigorous physical activity than women with other subtypes.
Post partum glycaemic status
The primary outcome was the prevalence of glucose intolerances (prediabetes) soon after delivery (at 6 to 9 weeks after delivery) after a GDM pregnancy in accordance with American Diabetes Association criteria (which is very different to our Australian criteria). Prediabetes can be impaired fasting glucose levels (IFG between 5.5 and 6.94 mol/L), impaired glucose tolerance (IGT; between 7.8 and 11 mmol/L), or both, ascertained by 2-hour, 75-g OGTT.
Overall, the prevalence of prediabetes at 6 to 9 weeks after delivery was 34.5% (9.9% IGT, 18.2% IFG, 6.5% both). The overall prevalence varied widely across GDM subtypes (p < 0.001):
- GD-P – 23.9%
- GD-F – 41.9% (prevalence ratio 1.74 X compared with GD-P)
- GD-M – 55.8% (prevalence ratio 2.23 X compared with GD-P)
To further breakdown the post partum trajectories, those with some IGT (isolated or mixed) are more likely to continue to have IGT post partum. Those with some IGT (isolated or both) are more likely to have continued IFG post partum. See Table 2.
The authors also explored the HOMA-IR and HOMA-B in these women. There was a continuous rise in HOMA-IR from women with GD-P to GD-F to GD-M. The HOMA-B were particular worse in women with GD-M.
What does this all mean?
The GD-P subtype
Post-load glucose intolerance predominantly reflects peripheral insulin resistance, whereby postprandial glucose levels remain elevated because of impaired glucose uptake by muscles (3,4). Reduced insulin sensitivity has indeed been associated with lower muscle mass (5,6) Although they did not directly measure muscle mass, women with GD-P participated in significantly less moderate-to-vigorous physical activity and had smaller waist circumferences than those with other subtypes. This might explain Asian women who tend to have less muscles are more likely to have GD-P.
Metabolically stressful events such as pregnancy may uncover or amplify these subclinical defects of peripheral insulin resistance as indicated by post-load glucose intolerance during an OGTT. The reversal of such defects may occur naturally after delivery in the GD-P subtype, with greater success when implementing lifestyle changes that increase muscle mass and peripheral sensitivity (7).
The GD-F subtype
Women with GD-F and especially GD-M had higher percentages of obesity and excessive weight gain during pregnancy. Fasting hyperglycaemia generally reflects hepatic insulin resistance, whereby the liver overproduces glucose because of insufficient suppression.27 Chronic inflammation stemming from visceral obesity is believed to be a top culprit for dysfunctional insulin signaling in the liver which aligns with the higher adiposity observed in the GD-F and GD-M subtypes (4).
GD-F and GD-M had similar prevalence of postpartum prediabetes after adjusting for GD treatment. These subtypes may achieve improved glycaemic control by combining early lifestyle and pharmacologic approaches that improve insulin sensitivity and mitigate obesity. These women are the ones that we need to monitor more intensively.
This study by Van Julie et al not only showed us the differenttrajectories of the difference subtypes of GDM, they also described the different characteristics of the women with the different GDM subtypes at baseline.
References:
- Van JAD, Lo JC, Zhu Y, et al. Early Postpartum Glucose Tolerance Reclassification by Gestational Diabetes Subtype. JAMA Netw Open. 2025;8(11):e2542668.
- Carpenter MW, Coustan DR. Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol. 1982;144(7):768-773.
- Petersen KF, Dufour S, Savage DB, et al. The role of skeletal muscle insulin resistance in the pathogenesis of the metabolic syndrome. Proc Natl Acad Sci U S A. 2007;104(31):12587-12594
- Mu W, Cheng XF, Liu Y, et al. Potential nexus of non-alcoholic fatty liver disease and type 2 diabetes mellitus: insulin resistance between hepatic and peripheral tissues. Front Pharmacol. 2019;9(JAN):1566
- Park JH, Lee MY, Shin HK, Yoon KJ, Lee J, Park JH. Lower skeletal muscle mass is associated with diabetes and insulin resistance: a cross-sectional study. Diabetes Metab Res Rev. 2023;39(7):e3681
- Minato-Inokawa S, Tsuboi-Kaji A, Honda M, et al. Low muscle mass is associated with low insulin sensitivity, impaired pancreatic β cell function, and high glucose excursion in nondiabetic nonobese Japanese women. Metabol Open. 2024;23:100306
- Ceysens G, Rouiller D, Boulvain M. Exercise for diabetic pregnant women. Cochrane Database Syst Rev. 2006;2006(3):CD004225