Table 3.

Associations of birth weight and gestational age with lung function in original units at ~17.5 years by sex in Hong Kong’s “Children of 1997” birth cohort (After inverse probability weighting and multiple imputation).

Sex	Exposures	FEV1, L				FVC, L				FEV1/FVC				FEF25–75%, L/s
		Crude		Model 1a		Crude		Model 1a		Crude		Model 1a		Crude		Model 1a
		β	95%CI	β	95%CI	β	95%CI	β	95%CI	β	95%CI	β	95%CI	β	95%CI	β	95%CI
Girls	Gestational age, w	0.02*	0.00 to 0.03	0.02*	0.00 to 0.03	0.01	−0.01 to 0.02	0.01	−0.01 to 0.02	0.00*	0.00 to 0.01	0.00*	0.00 to 0.01	0.05*	0.02 to 0.07	0.05*	0.02 to 0.07
	Preterm
	Full term birth	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—
	Preterm birth	−0.09	−0.20 to 0.02	−0.09	−0.21 to 0.02	0.00	−0.11 to 0.12	0.00	−0.12 to 0.11	−0.03*	−0.06 to −0.01	−0.03*	−0.06 to −0.01	−0.31*	−0.53 to −0.09	−0.31*	−0.53 to −0.09
	Birth weight, kg #	0.17*	0.11 to 0.22	0.18*	0.12 to 0.25	0.18*	0.12 to 0.23	0.22*	0.15 to 0.28	0.01	−0.01 to 0.02	0.00	−0.01 to 0.01	0.26*	0.15 to 0.36	0.22*	0.09 to 0.34
	Birth weight z-score b #	0.07*	0.05 to 0.09	0.07*	0.05 to 0.09	0.08*	0.06 to 0.11	0.08*	0.06 to 0.11	0.00	−0.01 to 0.02	0.00	−0.01 to 0.01	0.09*	0.04 to 0.13	0.08*	0.04 to 0.13
	Size for gestational age
	AGA	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—
	LGA	0.14*	0.06 to 0.21	0.14*	0.06 to 0.21	0.18*	0.11 to 0.26	0.18*	0.11 to 0.26	−0.01	−0.02 to 0.01	−0.01	−0.02 to 0.01	0.17*	0.02 to 0.31	0.16*	0.01 to 0.31
	SGA#	−0.11*	−0.19 to −0.03	−0.09*	−0.17 to −0.01	−0.11*	−0.19 to −0.03	−0.09*	−0.18 to −0.01	−0.01	−0.02 to 0.01	0.00	−0.01 to 0.01	−0.20*	−0.35 to −0.04	−0.18*	−0.34 to −0.02
Boys	Gestational age, w	0.00	−0.01 to 0.02	0.00	−0.01 to 0.02	0.00	−0.02 to 0.02	0.00	−0.02 to 0.02	0.00	0.00 to 0.00	0.00	0.00 to 0.00	0.02	−0.01 to 0.05	0.01	−0.02 to 0.04
	Preterm
	Full term birth	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—
	Preterm birth	−0.03	−0.14 to 0.08	−0.04	−0.15 to 0.08	0.00	−0.11 to 0.12	0.01	−0.12 to 0.14	−0.01*	−0.03 to 0.00	−0.01*	−0.03 to 0.00	−0.23*	−0.45 to −0.01	−0.23*	−0.45 to −0.01
	Birth weight, kg #	0.22*	0.16 to 0.28	0.31*	0.24 to 0.38	0.25*	0.18 to 0.32	0.36*	0.27 to 0.44	0.00	−0.01 to 0.01	0.00	−0.01 to 0.01	0.28*	0.16 to 0.39	0.35*	0.21 to 0.49
	Birth weight z-score b #	0.12*	0.09 to 0.15	0.12*	0.09 to 0.14	0.14	0.11 to 0.17	0.14*	0.11 to 0.17	0.00	0.00 to 0.00	0.00	0.00 to 0.00	0.13*	0.08 to 0.19	0.13*	0.07 to 0.18
	Size for gestational age
	AGA	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—	Ref	—
	LGA	0.21*	0.12 to 0.30	0.20*	0.11 to 0.30	0.22*	0.12 to 0.32	0.22*	0.11 to 0.32	0.00	−0.01 to 0.02	0.00	−0.01 to 0.02	0.30*	0.12 to 0.47	0.28*	0.11 to 0.45
	SGA#	−0.24*	−0.34 to −0.14	−0.24*	−0.34 to −0.14	−0.28*	−0.40 to −0.16	−0.28*	−0.39 to −0.16	0.00	−0.02 to 0.02	0.00	−0.02 to 0.02	−0.22*	−0.42 to −0.03	−0.21*	−0.40 to −0.01

Abbreviations: SGA, small-for-gestational age; AGA, appropriate-for-gestational age; LGA, large-for-gestational age; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; FEF_25–75%, forced expiratory flow at 25–75% of the pulmonary volume.

^aModel 1: Adjusted for age, birth order, maternal age at birth, maternal smoking, maternal birthplace, and parental social-economic positions (SEP, including household income, the highest parental occupation at recruitment and the highest parental occupation).

^bApart from the adjustment in footnote a, adjusted for gestational age.

^cFor average gestational age (39 weeks), the mean for birthweight of girls and boys are 3377 grams and 3433 grams respectively, and the SD for birthweight of girls and boys are 374 grams and 421 grams respectively. 

*Statistically significant association with lung function at the 0.05 level.

^#Statistically significant interaction with sex on FEV₁ and FVC.