Thirteen studies were included.
The effect of GDM treatment (Question 3) was evaluated in seven RCTs (n=2,797) plus one prospective cohort (n=3,986). Adverse effects of GDM screening (Question 4) were evaluated in two prospective cohort studies (n=309) and one cross-sectional study (n=118). Adverse effects of treatment (Question 5) were evaluated in six RCTs (n=1,845) and one prospective cohort study (n=301). No evidence was identified for the assessment of efficacy (Question 1) or diagnostic accuracy (Question 2) of screening tests for GDM.
Question 3. Does treatment for GDM reduce perinatal morbidity and mortality for the mother and/or infant?
Diagnosis and treatment versus no treatment after 24 weeks' gestation: one recent good-quality RCT (1,000 women with mild GDM diagnosed between 24 and 34 weeks' gestation) reported that treatment (advice about diet, self-monitoring with insulin if required) was associated with a statistically significant reduction in the composite neonatal outcome of any serious perinatal complication (death, shoulder dystocia, bone fracture and nerve palsy) compared with no treatment (adjusted relative risk, RR=0.33, 95% CI: 0.14, 0.75). Treatment also reduced pregnancy-induced hypertension or pre-eclampsia (adjusted RR 0.70, 95% CI: 0.51, 0.95). The study reported no evidence of harm. An earlier fair-quality RCT (in women at high risk of GDM) reported that treatment (10 units insulin per day) reduced macrosomia, but not perinatal deaths, compared with no treatment.
Diagnosis and treatment versus another treatment after 24 weeks' gestation: two RCTs reported that different types of intensified management (postprandial monitoring and insulin four times daily) were associated with significant reductions in perinatal complications (perinatal morbidity in one study, hyperbilirubinaemia, and macrosomia) compared with less intensive management; there was no evidence of significant maternal hypoglycaemia. The other three RCTs reported no difference between treatments in either glycaemic control achieved or outcomes.
Question 4. What are the adverse effects associated with screening for GDM?
There was limited and mixed evidence about the effects of screening on anxiety and quality of life. No adverse effects of screening on neonates were identified.
Question 5. What are the adverse effects associated with treatment for GDM?
The studies reported no maternal deaths and reports of maternal hypoglycaemia were rare. One RCT reported a significant reduction in postpartum depression amongst treated compared with untreated women. Limited data reported no harms to the foetus. There was no good evidence about potential harms to the neonate that were associated with treatment.