Table 1 Demographic and obstetric characteristics of the infants
Characteristic | n (%) or mean (SD) |
|---|---|
Month of birth, (n = 81,615) | |
January | 6,400 (7.8%) |
February | 5,736 (7.0%) |
March | 6,175 (7.6%) |
April | 6,308 (7.7%) |
May | 6,559 (8.0%) |
June | 6,292 (7.7%) |
July | 7,171 (8.8%) |
August | 8,190 (10.0%) |
September | 8,305 (10.2%) |
October | 7,691 (9.4%) |
November | 6,461 (7.9%) |
December | 6,327 (7.8%) |
Season of birth, (n = 81,615) | |
Spring (Apr–Jun) | 19,159 (23.5%) |
Summer (Jul–Sep) | 23,666 (29.0%) |
Autumn (Oct–Dec) | 20,479 (25.1%) |
Winter (Jan–Mar) | 18,311 (22.4%) |
Maternal age (years), (n = 81,611) | |
< 25 | 7,105 (8.7%) |
25–29 | 22,273 (27.3%) |
30–34 | 29,405 (36.0%) |
35–39 | 18,963 (23.2%) |
≥ 40 | 3,865 (4.7%) |
Annual household income (JPY), (n = 75,701) | |
< 4 million | 29,578 (39.1%) |
4 – < 6 million | 25,337 (33.5%) |
≥ 6 million | 20,786 (27.5%) |
Highest maternal educational level, (n = 80,778) | |
< 13 | 27,846 (34.5%) |
13 – 15 | 34,581 (42.8%) |
≥ 16 | 18,351 (22.7%) |
Maternal history of allergic disease, (n = 81,203) | |
Yes | 40,799 (50.2%) |
Maternal intake of vitamin D during pregnancy (μg), (n = 81,177) | |
Mean (SD) | 4.3 (2.8) |
Maternal active smoking during pregnancy, (n = 80,587) | |
Never-smokers | 47,828 (59.4%) |
Quit smoking before pregnancy | 19,133 (23.7%) |
Quit smoking during early pregnancy | 10,563 (13.1) |
Continued smoking | 3,063 (3.8%) |
Maternal passive smoking during pregnancy, (n = 80,979) | |
Almost never | 51,302 (63.4%) |
Less than 1 day per week | 9,712 (12.0%) |
2–3 days per week | 6,500 (8.0%) |
4–6 days per week | 3,877 (4.8%) |
Every day | 9,588 (11.8%) |
Infant sex, (n = 81,613) | |
Male | 41,903 (51.4%) |
Female | 39,710 (48.7%) |
Gestational weeks (w), (n = 81,459) | |
Mean (SD) | 38.9 (1.5) |
Feeding method during 1 month after birth, (n = 81,350) | |
Breastfeeding only | 34,548 (42.5%) |
Mixed feeding | 45,740 (56.2%) |
Infant formula only | 1,062 (1.3%) |
Presence of older siblings at 1 month after birth, (n = 81,615) | |
Yes | 42,695 (52.3%) |
Pet ownership, (n = 80,830) | |
Yes | 18,290 (22.6%) |
Registered regional center, (n = 81,615) | |
Hokkaido | 6,505 (8.0%) |
Miyagi | 6,700 (8.2%) |
Fukushima | 11,145 (13.7%) |
Chiba | 4,720 (5.8%) |
Kanagawa | 5,402 (6.6%) |
Koshin | 5,806 (7.1%) |
Toyama | 4,587 (5.6%) |
Aichi | 4,492 (5.5%) |
Kyoto | 3,247 (4.0%) |
Osaka | 6,268 (7.7%) |
Hyogo | 4,185 (5.1%) |
Tottori | 2,499 (3.1%) |
Kochi | 5,487 (6.7%) |
Fukuoka | 6,117 (7.5%) |
South Kyushu/Okinawa | 4,455 (5.5%) |