A network meta-analysis 3 included 32 RCTs assessing 6 kinds of treatments (metformin, metformin plus insulin, insulin, glyburide, acarbose, and placebo). Regarding the incidence of macrosomia and large for gestational age (LGA), metformin had lower incidence than glyburide (OR 0.54 and 0.4). In terms of the incidence of admission to the NICU, insulin had higher incidence compared with glyburide (OR 1.84). As for the incidence of neonatal hypoglycemia, metformin had lower incidence than insulin and glyburide (OR 0.63 and 0.39), and insulin was lower than glyburide (OR 0.62). For mean birth weight, metformin plus insulin was lower than insulin (SMD -0.58), glyburide (SMD -0.74), and placebo (SMD -0.66). Besides, metformin was observed to have lower birth weight than glyburide (SMD 0.26). As for weight gain, metformin and metformin plus insulin were lower than insulin (SMD -0.92 to -1.53). Metformin (plus insulin when required) had the lowest incidence of macrosomia, LGA, respiratory distress syndrome, low gestational age at delivery, and low birth weight.
A Cochrane review [Abstract] 1 included 8 studies with a total of 1418 patients. Caesarean section rate was not significantly different when comparing any specific treatment with routine antenatal care (ANC) (RR 0.94, 95% CI 0.80 to 1.12; 5 studies, n=1255). However, when comparing oral hypoglycaemics with insulin as treatment for GDM, there was a significant reduction (RR 0.46, 95% CI 0.27 to 0.77; 2 studies, n=90).
There was a reduction in the risk of pre-eclampsia with intensive treatment (including dietary advice and insulin) compared to routine ANC (RR 0.65, 95% CI 0.48 to 0.88; 1 study, n=1000). More women had their labours induced when given specific treatment compared to routine ANC (RR 1.33, 95% CI 1.13 to 1.57; 2 studies, n=1068). The composite outcome of perinatal morbidity (death, shoulder dystocia, bone fracture and nerve palsy) was significantly reduced for those receiving intensive treatment for mild GDM compared to routine ANC (RR 0.32, 95% CI 0.14 to 0.73; 1 study, n=1030).
There was a reduction in the proportion of infants weighing more than 4000 grams (RR 0.46, 95% CI 0.34 to 0.63; 1 study, n=1030) and the proportion of infants weighing greater than the 90th birth centile (RR 0.55, 95% CI 0.30 to 0.99; 3 studies, n=223) of mothers receiving specific treatment for GDM compared to routine ANC. However, there was no statistically significant difference in this proportion between infants of mothers receiving oral drugs compared to insulin as treatment for GDM.
Another Cochrane review [Abstract] 2 included 4 studies with a total of 543 women and their babies. Babies born to women receiving management for borderline GDM (generally dietary counselling and metabolic monitoring) were less likely to be macrosomic (birthweight greater than 4000 g) (RR 0.38, 95% CI 0.19 to 0.74; 3 trials, 438 infants) or large-for-gestational age (LGA) (RR 0.37, 95% CI 0.20 to 0.66; 3 trials, 438 infants) when compared with those in the routine care group. There were no significant differences in rates of caesarean section (RR 0.93, 95% CI 0.68 to 1.27; 3 trials, n=509) and operative vaginal birth (RR 1.37, 95% CI 0.20 to 9.27; 1 trial, n=83) between the two groups.
Comment: The quality of evidence is downgraded by study quality (inadequate or unclear allocation concealment and blinding).
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