Gestational diabetes mellitus (GDM) is associated with a wide range of adverse health consequences for women and their infants in the short and long term. With an increasing prevalence of GDM worldwide, there is an urgent need to assess strategies for GDM prevention, such as combined diet and exercise interventions. This is an update of a Cochrane review that was first published in 2015. To assess the effects of diet interventions in combination with exercise interventions for pregnant women for preventing GDM, and associated adverse health consequences for the mother and her infant/child. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (27 November 2016) and reference lists of retrieved studies. We included randomised controlled trials (RCTs) and cluster‐RCTs, comparing combined diet and exercise interventions with no intervention (i.e. standard care), that reported on GDM diagnosis as an outcome. Quasi‐RCTs were excluded. Cross‐over trials were not eligible for inclusion. We planned to include RCTs comparing two or more different diet/exercise interventions, however none were identified. Two review authors independently assessed study eligibility, extracted data, assessed the risk of bias of the included trials and assessed quality of evidence for selected maternal and infant/child outcomes using the GRADE approach. We checked data for accuracy. In this update, we included 23 RCTs (involving 8918 women and 8709 infants) that compared combined diet and exercise interventions with no intervention (standard care). The studies varied in the diet and exercise programs evaluated and health outcomes reported. None reported receiving funding from a drug manufacturer or agency with interests in the results. Overall risk of bias was judged to be unclear due to the lack of methodological detail reported. Most studies were undertaken in high‐income countries. For our primary review outcomes, there was a possible reduced risk of GDM in the diet and exercise intervention group compared with the standard care group (average risk ratio (RR) 0.85, 95% confidence interval (CI) 0.71 to 1.01; 6633 women; 19 RCTs; Tau² = 0.05; I² = 42%; P = 0.07; moderate‐quality evidence ). There was also a possible reduced risk of caesarean section (RR 0.95, 95% CI 0.88 to 1.02; 6089 women; 14 RCTs; moderate ‐ quality evidence). No clear differences were seen between groups for pre‐eclampsia (RR 0.98, 95% CI 0.79 to 1.22; 5366 participants; 8 RCTs; low‐quality evidence ), pregnancy‐induced hypertension and/or hypertension (average RR 0.78, 95% CI 0.47 to 1.27; 3073 participants; 6 RCTs; Tau² = 0.19; I² = 62%; very low‐quality evidence ), perinatal mortality (RR 0.82, 95% CI 0.42 to 1.63; 3757 participants; 2 RCTs; low‐quality evidence ) or large‐for‐gestational age (RR 0.93, 95% CI 0.81 to 1.07; 5353 participants; 11 RCTs; low‐quality evidence ). No data were reported for infant mortality or morbidity composite. Subgroup analyses (based on trial design, maternal body mass index (BMI) and ethnicity) revealed no clear differential treatment effects. We were unable to assess the impact of maternal age, parity and specific features of the diet and exercise interventions. Findings from sensitivity analyses (based on RCT quality) generally supported those observed in the main analyses. We were not able to perform subgroup analyses based on maternal age, parity or nature of the exercise/dietary interventions due to the paucity of information/data on these characteristics and the inability to meaningfully group intervention characteristics. For most of the secondary review outcomes assessed using GRADE, there were no clear differences between groups, including for perineal trauma (RR 1.27, 95% CI 0.78 to 2.05; 2733 participants; 2 RCTs; moderate‐quality evidence ), neonatal hypoglycaemia (average RR 1.42, 95% CI 0.67 to 2.98; 3653 participants; 2 RCTs; Tau² = 0.23; I² = 77%; low quality evidence ); and childhood adiposity (BMI z score) (MD 0.05, 95% CI ‐0.29 to 0.40; 794 participants; 2 RCTs; Tau² = 0.04; I² = 59%; low‐quality evidence ). However, there was evidence of less gestational weight gain in the diet and exercise intervention group compared with the control group (mean difference (MD) ‐0.89 kg, 95% CI ‐1.39 to ‐0.40; 5052 women; 16 RCTs; Tau² = 0.37; I² = 43%; moderate‐quality evidence ). No data were reported for maternal postnatal depression or type 2 diabetes ; childhood/adulthood type 2 diabetes, or neurosensory disability . Moderate‐quality evidence suggests reduced risks of GDM and caesarean section with combined diet and exercise interventions during pregnancy as well as reductions in gestational weight gain, compared with standard care. There were no clear differences in hypertensive disorders of pregnancy, perinatal mortality, large‐for‐gestational age, perineal trauma, neonatal hypoglycaemia, and childhood adiposity ( moderate‐ to very low‐quality evidence) . Using GRADE methodology, the evidence was assessed as moderate to very low quality. Downgrading decisions were predominantly due to design limitations (risk of bias), and imprecision (uncertain effect estimates, and at times, small sample sizes and low event rates), however two outcomes (pregnancy‐induced hypertension/hypertension and neonatal hypoglycaemia), were also downgraded for unexplained inconsistency (statistical heterogeneity). Due to the variability of the diet and exercise components tested in the included studies, the evidence in this review has limited ability to inform practice. Future studies could describe the interventions used in more detail, if and how these influenced behaviour change and ideally be standardised between studies. Studies could also consider using existing core outcome sets to facilitate more standardised reporting. Review question What are the effects of combined diet and exercise for preventing gestational diabetes mellitus (GDM), and related health problems for mothers and their babies? This is an update of a Cochrane review that was first published in 2015. Background GDM is high blood sugar (hyperglycaemia) during pregnancy. Up to a quarter of pregnant women develop GDM, with some at a higher risk than others (such as overweight or obese women, older women, and those of particular ethnicities). GDM can lead to significant health problems for women and their babies. In the short term, women with GDM may develop pre‐eclampsia (high blood pressure (hypertension) and protein in the urine), or give birth by caesarean section. Their babies may grow large for their gestational age, and, as a result, be injured at birth, and/or cause injury to their mothers during birth. Babies of mothers with GDM often have low blood glucose (hypoglycaemia) and are overweight. Later in life, health problems such as neurosensory disabilities and type 2 diabetes can develop in these babies. Eating well and exercising is known to prevent type 2 diabetes and may be effective for preventing GDM. Study characteristics We searched for evidence in November 2016 and included 23 randomised controlled trials (RCTs) (involving 8918 women and their 8709 babies). Most studies were undertaken in high‐income countries. All of the studies compared women receiving diet and exercise programs with women receiving standard care without diet and exercise programs. The studies varied in the diet and exercise programs evaluated and health outcomes reported. None reported receiving funding from a drug manufacturer or agency with interests in the results. Key results Findings from 19 studies (6633 women) showed a possible reduction in GDM in women who received diet and exercise programs compared with women who received standard care. Fourteen studies (6089 women) showed a possible reduction in caesarean birth (14 studies; 6089 women) and 16 studies (5052 women) showed lower weight gain during pregnancy in women who received exercise programs. We found no differences between groups in other health problems for: pre‐eclampsia (8 studies; 5366 women); high blood pressure (6 studies; 3073 women); a large for age baby at birth (11 studies; 5353 babies); and perineal trauma (2 studies; 2733 women). Death of babies around birth (2 studies; 3757 babies), the baby having low blood glucose after birth (2 studies; 3653 babies), and infants being overweight (2 studies; 794 infants) did not differ in the two groups. Effects on depression or type 2 diabetes for mothers, a combined outcome of death or ill‐health for babies, or type 2 diabetes or neurosensory disability for babies as children were not reported. Participant views of programs were examined. The evidence suggests combined diet and exercise programs may be effective for preventing GDM though the optimum components of these programs are not yet clear. Future studies could describe the interventions used in more detail, if and how these influenced behaviour change and ideally be standardised between studies. Studies could also consider measuring similar maternal and infant outcomes and report them in a standardised way. Quality of the evidence The overall risk of bias was judged unclear due to lack of information on methods. We assessed evidence quality using GRADE considerations for selected key outcomes. Our assessments ranged from moderate to very low.
