1. Additional data on lifestyle behavioural changes not reported according to definitions in the review methods.

Comparison 1. Preconception lifestyle advice on a combination of any of the following topics: weight, diet, vitamin and mineral intake, alcohol intake, caffeine intake, physical activity, smoking, and/or other substance abuse compared to routine care or attention control
	Reported behavioural changes in diet
Oostingh 2020	Number of participants with adequate vegetable intake (> 200 grams/d) at 6 months Women: 124/299 in experimental group 89/313 in control group RR 1.46, 95% CI 1.17 to 1.82 Men: 40/103 in experimental group 31/113 in control group RR 1.42, 95% CI 0.96 to 2.08 Number of participants with adequate fruit intake (> 2 pieces/d) at 6 months Women: 207/299 in experimental group 182/311 in control group RR 1.18, 95% CI 1.05 to 1.33 Men: 67/103 in experimental group 46/111 in control group RR 1.57, 95% CI 1.21 to 2.04
Ng 2018	Fruit intake in pieces/d at 3 months (mean ± SD) 2.82 ± 1.9 in experimental group (n = 131) 2.02 ± 1.7 in control group (n = 133) MD 0.80, 95% CI 0.36 to 1.24
Comparison 2. Preconception lifestyle advice on weight compared to routine care
	Reported behavioural changes in diet
Belan 2019	Composite score: healthy eating index in points at 6 months (mean ± SD) 18.2 ± 13.7 in experimental group (n = 46) 5.3 ± 12.4 in control group (n = 51) MD 12.90, 95% CI 7.68 to 18.12
Mutsaerts 2016	Sugary drinks in glasses/d at 6 months (mean ± SD) 0.59 ± 0.2 glasses/d in experimental group (n = 88) 0.99 ± 0.3 glasses/d in control group (n = 128) MD ‐0.41, 95% CI ‐0.47 to ‐0.34 Savoury snacks in handfuls/week at 6 months (mean ± SD) 2.17 ± 0.73 handfuls/week in experimental group (n = 100) 2.32 ± 0.81 handfuls/week in control group (n = 139) MD ‐0.15, 95% CI ‐0.35 to 0.05 Sweet snacks in portions/week at 6 months (mean ± SD) 1.725 ± 0.32 portion/week in experimental group (n = 99) 2.72 ± 0.79 portion/week in control group (n = 136) MD ‐1, 95% CI ‐1.14 to ‐0.85
	Reported behavioural changes in physical activity
Belan 2019	Total leisure activity energy expenditure in kcal/kg/d at 6 months (mean ± SD) 0.77 ± 1.63 in experimental group (n = 46) 0.17 ± 1.26 in control group (n = 51) MD 0.60, 95% CI 0.02 to 1.18
Comparison 3. Preconception lifestyle advice on alcohol intake compared to routine care
	Reported behavioural changes in alcohol intake
Rossi 2013	Decrease in number of drinks on a drinking day (mean ± SD) 1 ± 1 in experimental group (n = 16) 0.4 ± 1 in control group (n = 21) MD 0.60, 95% CI ‐0.05 to 1.25 Decrease in % of drinking days in past 6 months (mean ± SD) 0.2 ± 0.3 in experimental group (n = 16) 0.1 ± 0.2 in control group (n = 21) MD 0.10, 95% CI ‐0.07 to 0.27 Decrease in number of weeks drinking above the safety daily limit in the past 6 months(mean ± SD) 5.6 ± 9 in experimental group (n = 16) 1.7 ± 3.5 in control group (n = 21) MD 3.90, 95% CI ‐0.76 to 8.56 Decrease in number of binges in the past 6 months (mean ± SD) 14.5 ± 44.4 in experimental group (n = 16) 1.2 ± 4.5 in control group (n = 21) MD 13.30, 95% CI ‐8.54 to 35.14
Comparison 4. Preconception lifestyle advice on alcohol intake compared to routine care
	Reported behavioural changes in smoking
Hughes 2000	Delta stage‐of‐change = difference in stage of motivation to change smoking behaviour (mean) Experimental group (mean): 0.31 (no SD reported) (n = 47) Control group (mean): 0.26 (no SD reported) (n = 47) Rate of maintained cessation "Rate of maintained cessation rose from 4% to 24% (P < 0.001)" (experimental and control groups reported together) No further data provided

CI: confidence interval.

MD: mean difference.

RR: risk ratio.

SD: standard deviation.