A Cochrane review included 11 studies with a total of 2786 subjects. Dietary advice interventions versus standard care (6 trials): A trend towards a reduction in gestational diabetes mellitus (GDM) was observed for women receiving dietary advice . While no clear difference was observed for pre-eclampsia a reduction in pregnancy-induced hypertension and in gestational weight gain was observed . None of the trials reported on large-for-gestational age or neonatal mortality and morbidity. Physiological outcomes (oral glucose tolerance test, birth weight) did not differ in one trial (n=25) comparing high-fibre diet with control. Low glycaemic index diet compared to high glycaemic index diet (4 trials): No clear differences were shown in the risks of GDM, large for gestational age infants, caesarean section, or gestational weight gain .
| Outcome | Relative effect (95% CI) | Risk with standard care - Control | Risk with dietary advice interventions - Intervention (95% CI) | No of participants (studies) Quality of evidence |
|---|---|---|---|---|
| Gestational diabetes | RR 0.60 (0.35 to 1.04) | 126 per 1000 | 76 per 1000 (44 to 131) | 1279 (5) Very Low |
| Hypertensive disorders of pregnancy (pregnancy-induced hypertension) | RR 0.30 (0.10 to 0.88) | 98 per 1000 | 29 per 1000 (10 to 86) | 282 (2) Low |
| Hypertensive disorders of pregnancy (pre-eclampsia) | RR 0.61 (0.25 to 1.46) | 84 per 1000 | 51 per 1000 (21 to 123) | 282 (2) Low |
| Caesarean section | RR 0.98 (0.78 to 1.24) | 300 per 1000 | 294 per 1000 (234 to 372) | 1194 (4) Low |
| Gestational weight gain (kg) | MD -4.70 (-8.07 to -1.34) | The mean gestational weight gain in the intervention group was 4.7 kg less (- 8.07 kg to - 1.34 kg ) | 1336 (5) Low | |
| Outcome | Relative effect (95% CI) | Risk with moderate- to high-GI dietary advice - Control | Risk with low- GI dietary advice - Intervention (95% CI) | No of participants (studies) Quality of evidence |
|---|---|---|---|---|
| Gestational diabetes | RR 0.91 (0.63 to 1.31) | 110 per 1000 | 100 per 1000 (70 to 145) | 912 (4) Low |
| Caesarean birth | RR 1.27 (0.79 to 2.04) | 227 per 1000 | 288 per 1000 (179 to 463) | 201 (2) Very low |
| Gestational weight gain (kg) | MD -1.23 (-4.08 to 1.61) | The mean gestational weight gain in the intervention group was 1.23 kg less than in the control group (4.08 kg less to 1.61 more) | 787 (4) Very low | |
| Large-for-gestational age | RR 0.60 (0.19 to 1.86) | 114 per 1000 | 68 per 1000 (22 to 212) | 777 (3) Very low |
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and blinding of outcome assessment), by indirectness (few foetal outcomes), and by imprecise results (few patients and wide confidence intervals).