Table 1.

Baseline characteristics.

	n	Na	%
Age 5 years dataset (N = 984)
Female sex	494	984	50.2
Birth weight <2500 g	120	982	12.2
Gestational age <37 week	89	984	9
Maternal age ≥ 35 years	422	983	42.9
Cesarean delivery	251	982	25.6
Maternal education level, university	447	943	47.4
Income, >8,000,000 yen	429	897	47.8
Maternal allergy history	563	940	59.9
Age 9 years dataset (N = 729)
Female sex	365	729	50.1
Birth weight <2500 g	82	728	11.3
Gestational age <37 week	59	729	8.1
Maternal age ≥ 35 years	317	728	43.5
Cesarean delivery	178	727	24.5
Maternal education level, university	337	697	48.3
Income, >8,000,000 yen	316	664	47.6
Maternal allergy history	427	701	60.9

N: Number of participants.

N^a: Number of participants without missing values