Table 1.

Included study characteristics

First author and year	Study design, location and sample size	Maternal exposure(s)	Relevant child outcome(s) and age(s)	Quality assessment and overall rating for addressing the risk of bias (good/fair/poor)a
Adane 201829	Population-based prospective cohort study Australia n = 714 sibling pairs of children	Interpregnancy BMI changeb Calculated by taking BMI measures prior to the conception of each child and categorized: Stable, small gain, moderate gain, high gain	BMI categories based on age and sex-specific cut-offs for childrenb Second born children aged between 2 and 13 years	Positive Adjusts for maternal confounders Negative All exposure and outcome measures self-reported Lack of data on gestational age and gestational age gain Only 34% of women invited responded to the survey about their children Rating: Fair
Albers 201840	Individual patient data meta-analysis of 5 datasets from studies reporting BMI of children and the number of cigarettes smoked in pregnancy and then scanned for sibling data America (×3) Australia Canada n = 45 299 children from 14 231 families	Smoking status Number of cigarettes smoked across pregnancies b The number of siblings per family ranged from 2 to 16 children. There were two children for n = 10 576 families	BMI z-scores using the World Health Organization’s Child Growth Standardsd Age range of children in included studies 2–19 years. Mean age 5.61 (SD 2.37) years	Positive All five underlying studies assessed by the authors as being of good quality Adjusts for maternal confounders Negative Only able to use confounders used in most studies Rating: Fair
Aucott 201730	Population-based cohort (linkage) study Scotland n = 5863 mothers with more than one linked pregnancy and 718 sibling pairs of children	1. Smoking statusbRecorded at the start of each pregnancy and categorized: Never smoked, quit, started smoking, always smoked 2. Maternal weight change cBroken down into 7 categories from 10% or greater loss to 10% or greater gain. Reference category ±3.0%.	BMI categories using the International Obesity Task Force criteria for weight categories c BMI z-scores (derived using the 1990 UK standard)c Children mean age 5.6 (SD 0.6) years	Positive Routinely collected population level data for exposure and outcome Objectively measured outcome Adjusts for maternal confounders Excludes mothers >16 weeks pregnant at first antenatal appointment in order to exclude weight gain due to pregnancy Negative Smoking status self-reported at a single point in pregnancy only Maternal and child records only linked in 44% of cases Rating: Good
Barclay 201831	Population-based cohort (linkage) study Sweden n = 102 000	Length of the interpregnancy intervalc Defined here as the birth-to birth interval	BMI categories using standard cut-offs c Outcome measurements in men only, aged between 17 and 20 years at conscription Study based on full siblings only and in sibling groups of at least 3 Whole sibling groups used for measures of birth spacing, not just men	Positive Routinely collected population level data for exposure and outcome Objectively measured outcome Sibling groups included only where neither partner has children with a third partner Negative Men only for outcome measurement Based on sibling groups with at least 3 children Only maternal confounder controlled for is age Rating: Good
Devakumar 201632	Prospective cohort Brazil n = 2239	Length of the interpregnancy intervalb Defined as the period from the birth of the previous chid to the beginning of the pregnancy of the index child	Body composition; fat mass, fat-free mass, visceral fat, subcutaneous fatc BMIc Offspring mean age 30.2 years	Positives 68% follow-up rate at offspring age 30 years Objectively measured outcome Adjusts for maternal confounders Negatives Self-reported birth interval length based on maternal recall Rating: Fair
Huttly 199233	Longitudinal population-based cohort Brazil n = 2952	Length of the interpregnancy intervalb Here the interval since the preceding birth was recorded and is referred to as the ‘birth interval’	Weight for age and height z-scores, standardized to National Centre for health statistics standardsc Mean age 19 months	Positives 82% of eligible children have outcome data at mean age 19 months Objectively measured outcome Adjusts for maternal confounders Negatives Self-reported birth interval length based on maternal recall Does not report variance Rating: Fair
Iliadou 201034	Population-based cohort (linkage) study Sweden n = 8441 sibling pairs	Smoking statusb Recorded at the start of each pregnancy and categorized: non-smoker, smoking 1–9 cigarettes a day, smoking ≥10 cigarettes a day	BMIc Men only aged approximately 18 years at conscription	Positive Routinely collected population level data for outcome Objectively measured outcome Adjusts for maternal confounders Negative Men only for outcome measurement Smoking status self-reported at a single point in pregnancy only Rating: Good
Li 201835	Longitudinal cohort study America n = 2119	Length of the interpregnancy intervalc Defined as the date of the previous birth to the conception of the subsequent pregnancy	BMI z-scores standardized using US national reference datac Children aged 7 years	Positives Objectively measured outcome Adjusts for maternal confounders Negatives Study based on very old data with very young mothers; final child measurements taken in 1972 Total duration from recruitment to last birth only 6 years, limiting length of available birth intervals Rating: Poor
Smithers 201736	Population-based cohort (linkage) study Australia n = 4099	Birth by elective caesarean or by vaginal birth in the second pregnancy where the previous birth was by caesarean sectionc	Age and sex-specific BMI z-scores using the World Health Organization’s Child Growth Standardsc Children aged between 3 and 6 years	Positives Routinely collected population level data for exposure and outcome Objectively measured outcome Adjusts for maternal confounders Negatives No information on low linkage rates Rating: Good
Willmer 201337	Population-based cohort (linkage) study Sweden n = 71 sibling pairs	Maternal weight loss due to bariatric surgery between pregnanciesc	Measurements from child health Centre height and weight recorded at comprehensive check-up at age 4, and then predicted BMI at 4th birthday c Models also tried with BMIs converted to z-scores and with standardization against a British reference populationc	Positives Routinely collected population level data for exposure and outcome Objectively measured outcome Negatives Only 71 child–woman triads with complete data available for analysis Limited adjustments for maternal confounders Rating: Fair
Yuan 201638	Prospective cohort America n = 15 630	Birth method across successive pregnancies; caesarean or vaginalc	BMI for individuals under 18 years calculated using the International Obesity Task Force criteria for weight categoriesb For individuals over 18 years, obesity calculated using World Health Organization cut-offsb Offspring followed from age 9–14 years through age 20–28 years	Positives Controls for maternal confounders Negatives Self-reported outcome Rating: Fair

Abbreviations: BMI, body mass index (kg/m²); SD, standard deviation.

^aQuality was assessed using an adapted version of the National Heart, Lung and Blood Institute assessment tool for observational cohort and cross-sectional studies³⁹ and the PRISMA-IPD checklist.⁴¹

^bOutcome/exposure based on self-reported information

^cOutcome/exposure objectively measured

^dDetails of whether outcome/exposure measurements were self-reported or objectively measured are not stated