Background
Methods
Quality assessment and study inclusion
Statistical analysis
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BMI-GWG Interaction effect (exposure-mediator interaction);
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Natural direct effect: the effect on pregnancy outcomes that would result if we increased maternal BMI by 5 kg/m2 but held GWG constant;
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Natural indirect effect: the effect on pregnancy outcomes that would result if we held BMI constant but changed GWG to what it would have been with a 5 kg/m2 increase in BMI (roughly, the effect of BMI which is mediated via GWG); and
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Controlled direct effect at 6, 10, and 14 kg of GWG: the direct effect of BMI if we intervened such that all women had the relevant GWG. This effect will vary in the presence of exposure-mediator interaction.
Outcomes
Patient involvement
Results
Study selection
Study | Control | Intervention | Reason excluded |
---|---|---|---|
Barakat 2008 [25] | 70 | 72 | Post-randomisation exclusions from dataset (participants who discontinued intervention) |
Barakat 2011 [26] | 30 | 34 | Post-randomisation exclusions from dataset (participants who discontinued intervention) |
Barakat 2012 [27] | 151 | 137 | Post-randomisation exclusions from dataset (participants who discontinued intervention + others) |
El Beltagy 2013 [28] | 40 | 46 | Abstract only (no article), cannot verify randomisation/numbers |
Guelinckx 2010 [29] | 53 | 55 | Post-randomisation exclusions from dataset (‘dropouts’, participants developing GDM) |
Harrison 2013 [30] | 96 | 104 | GWG was measured at 28 weeks |
Hui 2011 [31] | 88 | 102 | Post-randomisation exclusions from dataset (participants who discontinued intervention) |
Khaledan 2010 [32] | 21 | 18 | Post-randomisation exclusions from dataset (GDM) |
Ong 2009 [33] | 6 | 7 | Birthweight missing for all participants |
Oostdam 2012 [34] | 39 | 41 | Post-randomisation exclusions from dataset (participants who discontinued intervention or developed blood glucose > 6) |
Perales 2015 [35] | 73 | 90 | Post-randomisation exclusions from dataset (participants who discontinued intervention + others) |
Perales 2016 [36] | 83 | 83 | Post-randomisation exclusions from dataset (participants who discontinued intervention + others) |
Prevedel 2003 [37] | 19 | 22 | Post-randomisation exclusions from dataset (participants who discontinued intervention + others) |
Wolff 2008 [38] | 30 | 26 | Post-randomisation exclusions from dataset (‘dropouts’, participants developing GDM) |
Yeo 2000 [39] | 8 | 8 | BMI missing for all participants |
Yeo unpub [40] | 12 | 6 | BMI missing for all participants |
Study | Control | Intervention |
---|---|---|
Althuizen 2013 [41] | 99 | 94 |
Baciuk 2008 [42] | 37 | 32 |
Bogaerts 2013 [23] | 138 | 58 |
Dodd 2014 [43] | 870 | 897 |
Haakstad 2011[44] | 40 | 41 |
Jeffries 2009 [45] | 110 | 122 |
Khoury 2005 [46] | 102 | 94 |
Luoto 2011 [21] | 165 | 215 |
Nascimento 2011 [47] | 40 | 37 |
Petrella 2014 [48] | 28 | 30 |
Phelan 2011 [49] | 193 | 190 |
Poston 2015 [50] | 619 | 576 |
Rauh 2013 [22] | 77 | 150 |
Renault 2014 [24] | 132 | 244 |
Ruiz 2013 [51] | 457 | 470 |
Sagedal 2017 [52] | 288 | 291 |
Stafne 2012 [53] | 340 | 385 |
Vinter 2011 [54] | 148 | 144 |
Vitolo 2011 [55] | 152 | 149 |
Walsh 2012 [56] | 335 | 319 |
Characteristic | Control | Intervention | Overall |
---|---|---|---|
Number of participants | 4370 | 4538 | 8908 |
BMI (kg/m2): mean (SD) | 29.28 (6.60) | 29.12 (6.70) | 29.20 (6.65) |
BMI category: N (%) | |||
18.5–24.9 | 1360 (31.12) | 1490 (32.83) | 2850 (31.99) |
25.0–29.9 | 1142 (26.13) | 1158 (25.52) | 2300 (25.82) |
≥ 30.0 | 1868 (42.75) | 1890 (41.65) | 3758 (42.19) |
Parity: N (%) | |||
0 | 2152 (49.24) | 2292 (50.51) | 4444 (49.89) |
1 + | 2213 (50.64) | 2245 (49.47) | 4458 (50.04) |
Missing | 5 (0.11) | 1 (0.02) | 6 (0.07) |
Maternal age: mean (SD) | 29.98 (5.19) | 30.10 (5.08) | 30.04 (5.13) |
Smoking: N (%) | |||
Non-smoker | 3339 (76.41) | 3535 (77.90) | 6874 (77.17) |
Smoker | 682 (15.61) | 661 (14.57) | 1343 (15.08) |
Missing | 349 (7.99) | 342 (7.54) | 691 (7.76) |
Findings
Mean difference (95% CI) | Odds ratio (95% CI) | |||
---|---|---|---|---|
Estimate | Infant birthweight | Infant birthweight z-score | LGA infant | Caesarean birth |
BMI-GWG interactiona | − 0.34 (− 0.88 to 0.19) | − 0.00 (− 0.00 to 0.00) | 1.00 (0.99 to 1.00) | 1.00 (1.00 to 1.00) |
Natural direct effectb | 65.56 (46.15 to 84.97) | 0.14 (0.10 to 0.18) | 1.38 (1.25 to 1.52) | 1.39 (1.27 to 1.52) |
Natural indirect effectc | − 14.21 (− 30.61 to 2.20) | − 0.03 (− 0.04 to − 0.01) | 0.96 (0.93 to 0.99) | 0.99 (0.97 to 1.01) |
Controlled direct effect at GWG 6 kgd | 57.54 (30.41 to 84.67) | 0.13 (0.08 to 0.18) | 1.45 (1.29 to 1.64) | 1.41 (1.26 to 1.59) |
Controlled direct effect at GWG 10 kgd | 47.84 (13.84 to 81.84) | 0.11 (0.04 to 0.18) | 1.46 (1.22 to 1.75) | 1.37 (1.17 to 1.61) |
Controlled direct effect at GWG 14 kgd | 40.64 (− 1.50 to 82.77) | 0.09 (0.00 to 0.18) | 1.47 (1.15 to 1.88) | 1.34 (1.10 to 1.65) |