Table 1. Distribution of maternal demographics by categories of birth weight among women who had a pregnancy.
| Total (N = 55,303) |
Missing on birth weight data (n = 8,938) |
Women with birth weight data (n = 46,365) |
Birth weight | P-valuec | |||||
|
| |||||||||
| <1,500 g (n = 365) |
1,500–2,499 g (n = 5,088) |
2,500–2,999 g (n = 26,099) |
3,000–3,999 g (n = 14,498) |
>4,000 g (n = 315) |
|||||
| N | n (%) | n | n (%) | n (%) | n (%) | n (%) | n (%) | ||
| Birth year | |||||||||
| 1936–1945 | 11,149 | 3,741 (33.6) | 7,408 | 95 (1.3) | 1,087 (14.7) | 4,846 (65.4) | 1,362 (18.4) | 18 (0.2) | <0.001 |
| 1946–1955 | 20,720 | 4,193 (20.2) | 16,527 | 155 (0.9) | 2,109 (12.8) | 10,772 (65.2) | 3,447 (20.9) | 44 (0.3) | |
| 1956–1965 | 14,484 | 850 (5.9) | 13,634 | 80 (0.6) | 1,195 (8.8) | 6,964 (51.1) | 5,298 (38.9) | 97 (0.7) | |
| 1966–1977 | 8,950 | 154 (1.7) | 8,796 | 35 (0.4) | 697 (7.9) | 3,517 (40.0) | 4,391 (49.9) | 156 (1.8) | |
| Age at first pregnancy, years | |||||||||
| 10–24 | 22,150 | 4,493 (20.3) | 17,657 | 154 (0.9) | 2,064 (11.7) | 10,534 (59.7) | 4,820 (27.3) | 85 (0.5) | <0.001 |
| 25–29 | 25,120 | 3,627 (14.4) | 21,493 | 167 (0.8) | 2,307 (10.7) | 12,071 (56.2) | 6,806 (31.7) | 142 (0.7) | |
| 30–34 | 5,669 | 533 (9.4) | 5,136 | 33 (0.6) | 518 (10.1) | 2,531 (49.3) | 1,991 (38.8) | 63 (1.2) | |
| ≥35 | 1,829 | 165 (9.0) | 1,664 | 10 (0.6) | 154 (9.3) | 741 (44.5) | 736 (44.2) | 23 (1.4) | |
| Missing | 535 | 120 (22.4) | 415 | 1 (0.2) | 45 (10.8) | 222 (53.5) | 145 (34.9) | 2 (0.5) | |
| BMI at 20 years, kg/m2 | |||||||||
| <18.5 | 6,540 | 685 (10.5) | 5,855 | 63 (1.1) | 827 (14.1) | 3,226 (55.1) | 1,707 (29.2) | 32 (0.5) | <0.001 |
| 18.5–24.9 | 42,595 | 5,916 (13.9) | 36,679 | 262 (0.7) | 3,809 (10.4) | 20,843 (56.8) | 11,521 (31.4) | 244 (0.7) | |
| ≥25.0 | 3,140 | 631 (20.1) | 2,509 | 29 (1.2) | 298 (11.9) | 1,314 (52.4) | 846 (33.7) | 22 (0.9) | |
| Missing | 3,028 | 1,706 (56.3) | 1,322 | 11 (0.8) | 154 (11.6) | 716 (54.2) | 424 (32.1) | 17 (1.3) | |
| Having an older brother or sister | |||||||||
| No | 19,791 | 2,468 (12.5) | 17,323 | 129 (0.7) | 1,989 (11.5) | 9,507 (54.9) | 5,585 (32.2) | 113 (0.7) | <0.001 |
| One | 15,787 | 2,100 (13.3) | 13,687 | 95 (0.7) | 1,329 (9.7) | 7,308 (53.4) | 4,835 (35.3) | 120 (0.9) | |
| More than one | 19,725 | 4,370 (22.2) | 15,355 | 141 (0.9) | 1,770 (11.5) | 9,284 (60.5) | 4,078 (26.6) | 82 (0.5) | |
| Maternal height, cm | |||||||||
| <151 | 14,034 | 3,600 (25.7) | 10,434 | 158 (1.5) | 1,885 (18.1) | 6,769 (64.9) | 1,605 (15.4) | 17 (0.2) | <0.001 |
| 151–155 | 16,712 | 2,769 (16.6) | 13,943 | 121 (0.9) | 1,598 (11.5) | 8,508 (61.0) | 3,670 (26.3) | 46 (0.3) | |
| 156–159 | 12,947 | 1,508 (11.6) | 11,439 | 53 (0.5) | 961 (8.4) | 6,209 (54.3) | 4,125 (36.1) | 91 (0.8) | |
| ≥160 | 11,226 | 843 (7.5) | 10,383 | 33 (0.3) | 613 (5.9) | 4,522 (43.6) | 5,054 (48.7) | 161 (1.6) | |
| Missing | 384 | 218 (56.8) | 166 | 0 (0.0) | 31 (18.7) | 91 (54.8) | 44 (26.5) | 0 (0.0) | |
| Family history of DM | 8,347 | 954 (11.4) | 7,393 | 57 (0.8) | 785 (10.6) | 3,912 (52.9) | 2,560 (34.6) | 79 (1.1) | <0.001 |
| Family history of HTN | 18,277 | 2,255 (12.3) | 16,022 | 107 (0.7) | 1,702 (10.6) | 8,811 (55.0) | 5,288 (33.0) | 114 (0.7) | <0.001 |
| Passive smoking at 10 years | |||||||||
| Almost none | 25,862 | 4,105 (15.9) | 21,757 | 156 (0.7) | 2,364 (10.9) | 12,548 (57.7) | 6,554 (30.1) | 135 (0.6) | <0.001 |
| 1–3 times a month | 2,067 | 189 (9.1) | 1,878 | 8 (0.4) | 191 (10.2) | 1,035 (55.1) | 625 (33.3) | 19 (1.0) | |
| 1–4 times a week | 4,139 | 394 (9.5) | 3,745 | 27 (0.7) | 336 (9.0) | 2,094 (55.9) | 1,263 (33.7) | 25 (0.7) | |
| Almost every day | 18,493 | 2,582 (14.0) | 15,911 | 120 (0.8) | 1,766 (11.1) | 8,556 (53.8) | 5,346 (33.6) | 123 (0.8) | |
| Missing | 4,742 | 1,668 (35.2) | 3,074 | 54 (1.8) | 431 (14.0) | 1,866 (60.7) | 710 (23.1) | 13 (0.4) | |
| Smoking status at first pregnancy a | |||||||||
| No | 48,534 | 8,407 (17.3) | 40,127 | 319 (0.8) | 4,454 (11.1) | 23,109 (57.6) | 11,997 (29.9) | 248 (0.6) | <0.001 |
| Yes | 6,543 | 490 (7.5) | 6,053 | 46 (0.8) | 611 (10.1) | 2,892 (47.8) | 2,438 (40.3) | 66 (1.1) | |
| Missing | 226 | 41 (18.1) | 185 | 0 (0.0) | 23 (12.4) | 98 (53.0) | 63 (34.1) | 1 (0.5) | |
| Educational attainment b | |||||||||
| Junior high school | 10,833 | 3,669 (33.9) | 7,164 | 116 (1.6) | 1,091 (15.2) | 4,731 (66.0) | 1,201 (16.8) | 25 (0.3) | <0.001 |
| High school | 27,902 | 3,797 (13.6) | 24,105 | 170 (0.7) | 2,612 (10.8) | 13,724 (56.9) | 7,457 (30.9) | 142 (0.6) | |
| Other | 12,923 | 976 (7.6) | 11,947 | 58 (0.5) | 1,100 (9.2) | 6,075 (50.8) | 4,601 (38.5) | 113 (0.9) | |
| University or more | 2,605 | 89 (3.4) | 2,516 | 13 (0.5) | 191 (7.6) | 1,168 (46.4) | 1,113 (44.2) | 31 (1.2) | |
| Missing | 1,040 | 407 (39.1) | 633 | 8 (1.3) | 94 (14.8) | 401 (63.3) | 126 (19.9) | 4 (0.6) | |
| Place of residence | |||||||||
| Yokote (Akita) | 14,418 | 2,784 (19.3) | 11,634 | 75 (0.6) | 1,196 (10.3) | 6,477 (55.7) | 3,791 (32.6) | 95 (0.8) | <0.001 |
| Saku (Nagano) | 14,813 | 2,405 (16.2) | 12,408 | 111 (0.9) | 1,428 (11.5) | 6,893 (55.6) | 3,906 (31.5) | 70 (0.6) | |
| Ninohe/Karumai (Iwate) | 4,894 | 952 (19.5) | 3,942 | 28 (0.7) | 548 (13.9) | 2,232 (56.6) | 1,107 (28.1) | 27 (0.7) | |
| Unzen/Minamishimabara (Nagasaki) |
5,513 | 826 (15.0) | 4,687 | 41 (0.9) | 410 (8.7) | 2,658 (56.7) | 1,538 (32.8) | 40 (0.9) | |
| Ozu (Ehime) | 3,504 | 384 (11.0) | 3,120 | 25 (0.8) | 363 (11.6) | 1,652 (52.9) | 1,054 (33.8) | 26 (0.8) | |
| Konan/Aki (Kochi) | 3,570 | 580 (16.3) | 2,990 | 33 (1.1) | 323 (10.8) | 1,724 (57.7) | 891 (29.8) | 19 (0.6) | |
| Chikusei (Ibaraki) | 8,591 | 1,007 (11.7) | 7,584 | 52 (0.7) | 820 (10.8) | 4,463 (58.8) | 2,211 (29.2) | 38 (0.5) | |
BMI, body mass index; DM, diabetes mellitus; HTN, hypertension.
afor smoking status at first pregnancy, “no” combines “never smoke or starting after the 1st pregnancy”;
bfor educational attainment, “other” means “junior college/specialty/4 year system dropout”;
cP-value excludes missing data.