Table 2.

The association between birthweight and childhood cancers, leukaemia, ALL, and non-leukaemia cancers in the pooled dataset

Birthweight metric (n cases)	Model 1b		Model 2c		Model 3d
	HRa	95% CI	HRa	95% CI	HRa	95% CI
Birthweight ≥4.0 kge
Cancer (377)	1.14	0.88, 1.48	1.19	0.91, 1.55	1.17	0.89, 1.54
Leukaemia (115)	1.25	0.80, 1.96	1.31	0.83, 2.08	1.21	0.74, 1.96
ALL (98)	1.21	0.74, 1.96	1.25	0.76, 2.06	1.21	0.72, 2.04
Non-leukaemia (262)	1.09	0.79, 1.50	1.14	0.82, 1.58	1.11	0.79, 1.56
Top 10% of birthweights in each cohortf
Cancer (377)	1.17	0.85, 1.61	1.22	0.88, 1.69	1.18	0.84, 1.65
Leukaemia (115)	1.25	0.72, 2.19	1.31	0.74, 2.31	1.16	0.63, 2.12
ALL (98)	1.14	0.61, 2.13	1.17	0.62, 2.23	1.08	0.55, 2.14
Non-leukaemia (262)	1.14	0.77, 1.68	1.18	0.80, 1.75	1.14	0.75, 1.71
Continuous birthweight, kgg
Cancer (377)	1.10	0.91, 1.31	1.26	1.02, 1.54	1.26	1.02, 1.56
Leukaemia (115)	1.25	0.89, 1.75	1.42	0.98, 2.06	1.35	0.90, 2.02
ALL (98)	1.16	0.81, 1.67	1.29	0.85, 1.93	1.29	0.83, 1.99
Non-leukaemia (262)	1.04	0.83, 1.28	1.19	0.93, 1.52	1.18	0.91, 1.54

^aHazard ratios (95% CI) from a stratified Cox proportional hazard regression using all observations in the pooled dataset. In models 2 and 3 missing observations are imputed using a chained multiple imputation method.

^bModel 1 is an unadjusted Cox proportional hazard regression model stratified by cohort in which birthweight is the only independent variable.

^cModel 2 is an adjusted Cox proportional hazard regression model stratified by cohort in which birthweight, gestational age, and sex of the child are the independent variables.

^d

Model 3 is an adjusted Cox proportional hazard regression stratified by cohort in which, for:

1. Cancer: birthweight hazard ratio is adjusted for gestational age, child’s sex, maternal age, paternal age (rescaled as quadratic), first born, and maternal pre-pregnancy BMI.
2. Leukaemia: birthweight hazard ratio is adjusted for gestational age, child’s sex, maternal age, total pregnancy weight gain, maternal pre-pregnancy BMI, first born, and any maternal smoking during pregnancy.
3. ALL: birthweight hazard ratio is adjusted for gestational age, child’s sex, paternal age (rescaled as quadratic), total pregnancy weight gain, and any maternal smoking during pregnancy.
4. Non-leukaemia cancers: birthweight hazard ratio is adjusted for gestational age, child’s sex, paternal age (rescaled as quadratic), total pregnancy weight gain, first born, and maternal pre-pregnancy BMI.

^eReference group for birthweight ≥4.0 kg is birthweight <4.0 kg.

^fThe reference group for the top 10% of each cohort is the bottom 90% of each cohort.

^gFor continuous birthweight, the hazard ratio represents a 1 kg increase in birthweight.