Table 1.

Summary of studies included in final review

Study	N	Exposure definition and age window	Outcome and age of measurement	Anthropometric reference used for outcome definition	Covariates adjusted for
Saari et al. [33]	12 062	Any antibiotic at <24 months	Adjusted difference (β) in zBMI at ⩾24 months	Finnish growth reference	Maternal smoking after first trimester, parental relationship, mode of delivery, birth weight and length (length for boys only)
			aOR for overweight at ⩾24 months
Murphy et al. [24]	74 946	Any antibiotic at <12 months	Adjusted difference (β) in BMI at 5–8 years		Age, sex, BMI measurement type (parental report or objective measurement) (see Statistical methodology column), maternal smoking, breastfeeding, current wheeze, early life paracetamol use, gross national income (tested for interaction only)
Trasande et al. [26]	11 532	Any antibiotic at ⩽24 months	Adjusted difference (β) in zBMI at 38 months and 7 years	British 1990 growth reference	Birth weight, maternal parity, maternal race, maternal social class, maternal education, parental BMI (pre-pregnancy and later), first trimester smoking, breastfeeding, timing of introduction of complementary foods, time per day watching television, in car on weekdays and weekends, dietary patterns at 38 months, sleep duration at 7 years
			aOR for overweight at 38 months and 7 years
Ajslev et al. [22]	28 354	Any antibiotic at <6 monthsa	aOR for overweight at 7 years	International Obesity Task Force reference (2007, 2012)	Maternal age, socioeconomic status, pre-pregnancy BMI, gestational weight gain, smoking, paternal BMI, parity, birth weight, sex, exclusive breastfeeding and age at 7 year follow-up
Bailey et al. [30]	64 580	Any antibiotic at ⩽23 months	Adjusted hazard ratio for obesity at 24–59 months	Centers for Disease Control and Prevention 2000 reference	Race/ethnicity, age at first primary care visit and number of primary care visits, sex, practice location at first visit, insurance coverage, common childhood infection diagnoses in first 2 years, calendar year and practice of first entry to primary care system, oral steroids and anti-reflux medication
Azad et al. [23]	616	Any antibiotic at <12 months	aOR for overweight at 9 years	Centers for Disease Control and Prevention 2000 reference	Sex, birth weight, breastfeeding, maternal overweight, smoke exposure at birth, family income, sibship, diet, physical activity, current asthma, maternal asthma
			aOR for overweight at 12 years
Rogawski et al. [27]	497	Any antibiotic at <6 months	Adjusted difference (β) in weight-for-length z-score at 6 months to 3 years	World Health Organization 2006 standards	Sex, prior growth z-score (measured at the beginning of the month), socioeconomic status, maternal education, household hygiene, household crowding, low birth weight, preterm birth, caesarean delivery, exclusive breastfeeding, number of days with infection/severe illness, number of days with diarrhoea, number of severe diarrhoea events, dehydration during diarrhoea, oral rehydration, hospitalisation events, days with diarrhoea in the previous month
Schwartz et al. [25]	1 63 820	Any (and cumulative) antibiotic at ⩽18 years	Adjusted difference (β) in BMI at ⩽18 years		Age, sex, race/ethnicity, medical assistance
Gerber et al. [29]	38 522	Any antibiotic at <6 months	Adjusted difference in rate of weight gain (%) between 2 and 5 years		Singleton analysis: adjustments made for both mean-level covariates (sex, birth weight, race, Medicaid insurance status, number of siblings, birth year, baseline length, primary care site) and rate-level covariates (as above, excluding primary care site) Twin analysis: sex, birth weight, baseline length
Li et al. [32]	2 60 556	Any antibiotic at <12 months among children with infection	aOR for obesity at 2–18 years	Centers for Disease Control and Prevention 2000 reference	Infection type and number of episodes (diagnoses >2 weeks apart), maternal age and race/ethnicity, pre-pregnancy BMI, preterm delivery, sex, low birth weight, maternal antibiotic use and infections during pregnancy, maternal education, marital status, smoking during pregnancy, mode of delivery, timing of initial prenatal care, gestational or pre-existing diabetes, breastfeeding
Scott et al. [21]	21 714	Any antibiotic at <24 months	aOR for obesity at 4 years	British 1990 growth referenceb	Maternal obesity, maternal diabetes, mode of delivery, socioeconomic status, year and country of birth, urban dwelling and sibling obesity
Mbakwa et al. [31]	979	Any antibiotic at ⩽10 years	Adjusted difference (β) in zBMI at ⩽10 years	Dutch growth reference	Study recruitment group, household size, maternal education, maternal pre-pregnancy weight, maternal pregnancy weight gain, smoking during pregnancy, gestational diabetes, gestational hypertension, mode and place of delivery, sex, birth weight, gestational age, duration of breastfeeding, child's dietary intake and physical activity
			aOR for overweight at ⩽10 years
Rogawski et al. [28]	1954	7-day increase in antibiotic exposure duration at <6 months	Adjusted difference (β) in WAZ at 6 months to 2 years	World Health Organization 2006 standards	Site, child's sex, enrolment weight-for-age, WAMI (water, assets maternal education and income) score, household crowding, maternal height, maternal education, characteristics of child's first 6 months (percent days exclusively breast-fed, number of diarrhoea episodes, days with fever or vomiting or respiratory illnesses, presence of acute lower respiratory infection or bloody stools and hospitalisation)

zBMI, body mass index-for-age z-score; WAZ, weight-for-age z-score; aOR, adjusted odds ratio.

*p < 0.05.

See Supplementary Tables S2 and S3 for full details on characteristics of studies.

Blank cells for anthropometric reference column indicate that none was used.

^aAuthors reported that questionnaires were only able to capture antibiotics prescribed for ear and lung infection.

^bBritish 1990 growth reference used as part of the UK WHO Term Growth Reference.