Glycemic thresholds used to diagnose gestational diabetes mellitus (GDM) are a continued subject of debate. Lower glycemic thresholds identify women with milder GDM for whom treatment benefit is unclear. We compared adverse maternal and neonatal outcomes in treated and untreated women with mild hyperglycemia.

We reviewed 11 553 patient charts from two tertiary care centers and included singleton pregnancies >32-week gestation. GDM was diagnosed using the one- or two-step 75 g oral glucose tolerance test (OGTT) depending on the center. All OGTT results were reviewed. Women with glycemic values falling between the thresholds of the two tests, referred to as intermediate hyperglycemic (IH), defined as FPG 5.1–5.2 mmol/L, 1 h PG 10.0–10.5 mmol/L, or 2 h PG 8.5–8.9 mmol/L at 75 g OGTT, were untreated at center A and treated at center B.

There were 630 women with IH, 334 were untreated (center A) and 296 who were treated (center B). After adjusting for covariates, untreated IH women had significantly higher rates of gestational hypertension (aOR 6.02, P = 0.002), large for gestational age (LGA) (aOR 3.73, P < 0.001) and birthweights > 4000 g (aOR 3.35, P = 0.001). Our results indicate that treating 11 women with IH would prevent one LGA birth and treating 13 would prevent 1 birthweight > 4000 g.

The diagnosis of GDM using the two-step OGTT fails to identify subgroups of women with mild hyperglycemia that would benefit from treatment to lower the risk for adverse maternal and neonatal outcomes. Treatment of women with mild hyperglycemia decreased the risk of LGA and birthweight >4000 g by 3-fold.