Abstract: We included two trials that randomised 4523 women and their infants. Both trials were conducted in Ireland. One trial (which quasi-randomised 3742 women, and analysed 3152 women) compared universal screening versus risk factor-based screening, and one trial (which randomised 781 women, and analysed 690 women) compared primary care screening versus secondary care screening. We were not able to perform meta-analyses due to the different interventions and comparisons assessed. Overall, there was moderate to high risk of bias due to one trial being quasi-randomised, inadequate blinding, and incomplete outcome data in both trials. We used GRADEpro GDT software to assess the quality of the evidence for selected outcomes for the mother and her child. Evidence was downgraded for study design limitations and imprecision of effect estimates. Universal screening versus risk-factor screening (one trial) Mother More women were diagnosed with GDM in the universal screening group than in the risk-factor screening group (risk ratio (RR) 1.85, 95% confidence interval (CI) 1.12 to 3.04; participants = 3152; low-quality evidence). There were no data reported under this comparison for other maternal outcomes including hypertensive disorders of pregnancy, caesarean birth, perineal trauma, gestational weight gain, postnatal depression, and type 2 diabetes. Child Neonatal outcomes: large-for-gestational age, perinatal mortality, mortality or morbidity composite, hypoglycaemia; and childhood/adulthood outcomes: adiposity, type 2 diabetes, and neurosensory disability, were not reported under this comparison. Primary care screening versus secondary care screening (one trial) Mother There was no clear difference between the primary care and secondary care screening groups for GDM (RR 0.91, 95% CI 0.50 to 1.66; participants = 690; low-quality evidence), hypertension (RR 1.41, 95% CI 0.77 to 2.59; participants = 690; low-quality evidence), pre-eclampsia (RR 0.80, 95% CI 0.36 to 1.78; participants = 690;low-quality evidence), or caesarean section birth (RR 1.00, 95% CI 0.80 to 1.27; participants = 690; low-quality evidence). There were no data reported for perineal trauma, gestational weight gain, postnatal depression, or type 2 diabetes. Child There was no clear difference between the primary care and secondary care screening groups for large-for-gestational age (RR 1.37, 95% CI 0.96 to 1.96; participants = 690; low-quality evidence), neonatal complications: composite outcome, including: hypoglycaemia, respiratory distress, need for phototherapy, birth trauma, shoulder dystocia, five minute Apgar less than seven at one or five minutes, prematurity (RR 0.99, 95% CI 0.57 to 1.71; participants = 690; low-quality evidence), or neonatal hypoglycaemia (RR 1.10, 95% CI 0.28 to 4.38; participants = 690; very low-quality evidence). There was one perinatal death in the primary care screening group and two in the secondary care screening group (RR 1.10, 95% CI 0.10 to 12.12; participants = 690; very low-quality evidence). There were no data for neurosensory disability, or childhood/adulthood adiposity or type 2 diabetes. There are insufficient randomised controlled trial data evaluating the effects of screening for GDM based on different risk profiles and settings on maternal and infant outcomes. Low-quality evidence suggests universal screening compared with risk factor-based screening leads to more women being diagnosed with GDM. Low to very low-quality evidence suggests no clear differences between primary care and secondary care screening, for outcomes: GDM, hypertension, pre-eclampsia, caesarean birth, large-for-gestational age, neonatal complications composite, and hypoglycaemia. Further, high-quality randomised controlled trials are needed to assess the value of screening for GDM, which may compare different protocols, guidelines or programmes for screening (based on different risk profiles and settings), with the absence of screening, or with other protocols, guidelines or programmes. There is a need for future trials to be sufficiently powered to detect important differences in short- and long-term maternal and infant outcomes, such as those important outcomes pre-specified in this review. As only a proportion of women will be diagnosed with GDM in these trials, large sample sizes may be required.

Plain-language summary: We searched for evidence (January 2017) and included two trials involving 4523 women and their babies. Both trials were conducted in Ireland and were at a moderate to high risk of bias. We could not combine the data from these trials because they looked at different interventions and comparisons. One compared ‘universal’ screening with ‘risk factor’-based screening for GDM. The other compared screening women at their general practitioners' clinic (primary care) versus at the hospital (secondary care). In one trial (with information available for 3152 women), more women were diagnosed with GDM in the group of women who received ‘universal’ screening, compared with the group of women with ‘risk factor’-based screening (low-quality evidence). The trial did not report on outcomes relating to the mothers, including high blood pressure disorders of pregnancy, caesarean birth, perineal trauma, weight gain in pregnancy, postnatal depression, and type 2 diabetes. The trial did not report outcomes relating to the babies including being born large-for-gestational age, death (before or shortly after birth), death or a serious complication, hypoglycaemia, or adiposity, type 2 diabetes, and disability in childhood or adulthood. In the second trial (with information available for 690 women), screening at the general practitioner's clinic versus the hospital did not make a clear difference to the number of women diagnosed with GDM (low-quality evidence), high blood pressure (low-quality evidence), pre-eclampsia (low-quality evidence), or the number who had a caesarean birth (low-quality evidence). This trial did not report perineal trauma, weight gain in pregnancy, postnatal depression, or type 2 diabetes. Screening at the general practitioner's clinic versus at the hospital did not make a clear difference to the number of babies born large-for-gestational age (low-quality evidence), death (before or shortly after birth), death or a serious complication (low-quality evidence), or hypoglycaemia (very low-quality evidence). Childhood or adulthood adiposity, type 2 diabetes, and disability were not reported in the trial. There is not enough evidence to guide us on effects of screening for GDM based on different risk profiles or settings on outcomes for women and their babies. Further large, well-designed, randomised controlled trials are required to assess important short- and long-term outcomes for mothers and their babies.