Table 2. Baseline profiles of mothers in the JECS Main Study and Sub-Cohort Study.
| Variables | JECS Sub-Cohort Study | JECS Main Studya | ||||
|
| ||||||
| Number of valid response | n | (%) | Number of valid response | n | (%) | |
| Number of pregnancies | 4,986 | 100,778 | ||||
| Age at delivery, years | 4,985 | 100,768 | ||||
| Total, mean (SD) | 4,985 | 31.9 (4.9) | 100,768 | 31.2 (5.1) | ||
| <20 | 17 | 0.3 | 893 | 0.9 | ||
| 20–24 | 339 | 6.8 | 9,229 | 9.2 | ||
| 25–29 | 1,241 | 24.9 | 27,686 | 27.5 | ||
| 30–34 | 1,791 | 35.9 | 35,571 | 35.3 | ||
| 35–39 | 1,295 | 26.0 | 22,713 | 22.5 | ||
| ≥40 | 302 | 6.1 | 4,676 | 4.6 | ||
| Marital status | 4,973 | 98,312 | ||||
| Married | 4,809 | 96.7 | 94,032 | 95.6 | ||
| Unmarried | 132 | 2.7 | 3,444 | 3.5 | ||
| Divorced/widowed | 32 | 0.6 | 836 | 0.9 | ||
| Family composition | 4,960 | 98,123 | ||||
| One-person households | 24 | 0.5 | 653 | 0.7 | ||
| A couple only | 1,567 | 31.6 | 30,105 | 30.7 | ||
| A couple with their child(ren) | 2,299 | 46.4 | 43,556 | 44.4 | ||
| A parent with his or her child(ren) | 25 | 0.5 | 848 | 0.9 | ||
| Other households | 1,045 | 21.1 | 22,961 | 23.4 | ||
| Educational background, years | 4,962 | 97,004 | ||||
| <10 | 188 | 3.8 | 4,704 | 4.8 | ||
| 10–12 | 1,357 | 27.3 | 30,544 | 31.5 | ||
| 13–16 | 3,343 | 67.4 | 60,333 | 62.2 | ||
| ≥17 | 74 | 1.5 | 1,423 | 1.5 | ||
| Paternal educational background, years | 4,945 | 96,387 | ||||
| <10 | 281 | 5.7 | 7,049 | 7.3 | ||
| 10–12 | 1,656 | 33.5 | 35,515 | 36.8 | ||
| 13–16 | 2,731 | 55.2 | 49,483 | 51.3 | ||
| ≥17 | 277 | 5.6 | 4,340 | 4.5 | ||
| Household income, million Japanese-yen/year | 4,762 | 90,596 | ||||
| <2 | 221 | 4.6 | 5,140 | 5.7 | ||
| 2 to <4 | 1,544 | 32.4 | 31,311 | 34.6 | ||
| 4 to <6 | 1,634 | 34.3 | 29,942 | 33.1 | ||
| 6 to <8 | 786 | 16.5 | 14,410 | 15.9 | ||
| 8 to <10 | 357 | 7.5 | 5,926 | 6.5 | ||
| ≥10 | 220 | 4.6 | 3,867 | 4.3 | ||
| Occupation in early pregnancy | 4,948 | 97,935 | ||||
| Administrative and managerial workers | 25 | 0.5 | 567 | 0.6 | ||
| Professional and engineering workers | 1,208 | 24.4 | 21,857 | 22.3 | ||
| Clerical workers | 811 | 16.4 | 16,432 | 16.8 | ||
| Sales workers | 265 | 5.4 | 5,744 | 5.9 | ||
| Service workers | 732 | 14.8 | 15,527 | 15.9 | ||
| Security workers | 17 | 0.3 | 242 | 0.2 | ||
| Agriculture, forestry and fishery workers | 26 | 0.5 | 454 | 0.5 | ||
| Manufacturing process workers | 119 | 2.4 | 3,376 | 3.4 | ||
| Transport and machine operation workers | 9 | 0.2 | 177 | 0.2 | ||
| Construction and mining workers | 4 | 0.1 | 71 | 0.1 | ||
| Carrying, cleaning, packaging, and related workers | 41 | 0.8 | 678 | 0.7 | ||
| Homemaker | 1,490 | 30.1 | 28,225 | 28.8 | ||
| Others (students, inoccupation, workers not classifiable by occupation) | 201 | 4.1 | 4,585 | 4.7 | ||
| Smoking habits | 4,984 | 99,053 | ||||
| Never smoked | 3,068 | 61.6 | 57,444 | 58.0 | ||
| Ex-smokers who quit before pregnancy | 1,206 | 24.2 | 23,571 | 23.8 | ||
| Smokers during early pregnancy | 710 | 14.3 | 18,038 | 18.2 | ||
| Passive smoking (presence of smokers at home)b | 4,245 | 79,910 | ||||
| No | 3,697 | 87.1 | 66,486 | 83.2 | ||
| Yes | 548 | 12.9 | 13,424 | 16.8 | ||
| Alcohol consumption | 4,986 | 99,149 | ||||
| Never drank | 1,675 | 33.6 | 34,279 | 34.6 | ||
| Ex-drinkers who quit before pregnancy | 941 | 18.9 | 19,392 | 19.6 | ||
| Drinkers during early pregnancy | 2,370 | 47.5 | 45,478 | 45.9 | ||
| Body mass index before pregnancy | 4,985 | 100,538 | ||||
| <18.5 kg/m2 | 794 | 15.9 | 16,272 | 16.2 | ||
| 18.5–24.9 kg/m2 | 3,657 | 73.4 | 73,416 | 73.0 | ||
| ≥25 kg/m2 | 534 | 10.7 | 10,850 | 10.8 | ||
| Parity | 4,968 | 100,288 | ||||
| 0 | 2,058 | 41.4 | 41,573 | 41.5 | ||
| 1 | 1,900 | 38.2 | 38,281 | 38.2 | ||
| ≥2 | 1,010 | 20.3 | 20,434 | 20.4 | ||
SD, standard deviation.
aMichikawa et al, J Epidemiol 2018;28(2):99–104 (reference No. 2).
bExcluding smokers during early pregnancy.