Table 1.
Baseline characteristics of the participants in the Japan Environment and Children’s Study (2011–2014).
| No. of womena | Sleep duration during preconception (h) | No. of womena | Sleep duration during pregnancy (h) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| < 6 | 6–7 | 7–8 | 8–9 | 9–10 | > 10 | < 6 | 6–7 | 7–8 | 8–9 | 9–10 | > 10 | |||
| (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | |||
| No. of women | 87,106 | 6,028 | 17,260 | 29,350 | 21,521 | 8,830 | 4,117 | 86,358 | 4,305 | 12,948 | 26,769 | 24,491 | 12,166 | 5,679 |
| Age at delivery (years) | ||||||||||||||
| < 25 | 8,499 | 10.3 | 7.7 | 8.0 | 9.3 | 12.4 | 27.1 | 8,465 | 11.7 | 8.6 | 8.0 | 8.5 | 11.1 | 22.7 |
| 25–29 | 24,039 | 25.5 | 26.8 | 27.6 | 27.9 | 28.7 | 30.3 | 23,838 | 25.4 | 26.3 | 27.2 | 27.7 | 28.6 | 31.6 |
| 30–34 | 30,809 | 32.0 | 35.4 | 36.5 | 36.5 | 35.3 | 26.6 | 30,591 | 31.3 | 34.3 | 36.3 | 36.7 | 36.7 | 28.8 |
| ≥ 35 | 23,759 | 32.2 | 30.2 | 28.0 | 26.3 | 23.6 | 16.0 | 23,464 | 31.5 | 30.8 | 28.5 | 27.2 | 23.7 | 16.9 |
| Smoking habits | ||||||||||||||
| Never-smokers | 50,646 | 52.8 | 60.3 | 60.4 | 58.4 | 55.8 | 46.4 | 50,269 | 53.7 | 59.5 | 60.1 | 59.1 | 56.7 | 50.3 |
| Ex-smokers who quit before pregnancy | 20,358 | 20.7 | 21.7 | 23.0 | 24.7 | 26.1 | 24.8 | 20,184 | 21.3 | 21.8 | 22.7 | 24.0 | 25.6 | 24.6 |
| Smokers during early pregnancy | 15,979 | 26.4 | 18.1 | 16.6 | 16.9 | 18.1 | 28.8 | 15,788 | 25.0 | 18.7 | 17.2 | 16.9 | 17.7 | 25.1 |
| Alcohol consumption | ||||||||||||||
| Never-drinkers | 29,955 | 31.9 | 32.8 | 34.2 | 35.8 | 36.0 | 35.7 | 29,702 | 33.0 | 33.6 | 34.1 | 34.8 | 35.3 | 35.1 |
| Ex-drinkers who quit before pregnancy | 16,233 | 17.1 | 16.7 | 17.8 | 19.7 | 22.5 | 21.7 | 15,767 | 17.9 | 16.2 | 17.6 | 18.4 | 20.7 | 21.1 |
| Drinkers during early pregnancy | 40,885 | 51.1 | 50.5 | 48.0 | 44.6 | 41.5 | 42.7 | 40,859 | 49.2 | 50.2 | 48.4 | 46.8 | 44.0 | 43.9 |
| Pre-pregnancy body mass index (kg/m2) | ||||||||||||||
| < 18.5 | 14,045 | 15.8 | 16.1 | 16.0 | 16.2 | 15.8 | 18.0 | 13,969 | 16.9 | 15.9 | 16.0 | 15.8 | 16.7 | 17.6 |
| 18.5–24.9 | 63,883 | 72.4 | 73.8 | 73.6 | 73.5 | 73.3 | 71.0 | 63,334 | 71.4 | 73.7 | 74.0 | 73.9 | 72.4 | 71.3 |
| ≥ 25.0 | 9,140 | 11.8 | 10.2 | 10.4 | 10.3 | 10.9 | 11.0 | 9,000 | 11.8 | 10.5 | 10.0 | 10.3 | 11.0 | 11.1 |
| Parity | ||||||||||||||
| 0 | 37,911 | 57.8 | 57.6 | 47.3 | 32.1 | 24.1 | 41.0 | 37,640 | 55.3 | 57.0 | 48.7 | 36.5 | 29.1 | 44.0 |
| ≥ 1 | 48,900 | 42.2 | 42.4 | 52.7 | 67.9 | 75.9 | 59.0 | 48,407 | 44.7 | 43.0 | 51.3 | 63.5 | 70.9 | 56.0 |
| Current history | ||||||||||||||
| Diabetes or gestational diabetes | 2,665 | 3.5 | 3.2 | 3.0 | 2.9 | 3.1 | 3.2 | 2,638 | 3.9 | 3.2 | 3.1 | 2.9 | 3.0 | 3.1 |
| Hypertensive disorders in pregnancy | 2,759 | 4.5 | 3.7 | 3.2 | 2.7 | 2.4 | 3.0 | 2,618 | 4.0 | 3.6 | 3.1 | 2.8 | 2.6 | 2.6 |
| Intrauterine infection | 612 | 1.0 | 0.8 | 0.7 | 0.6 | 0.5 | 0.8 | 554 | 0.7 | 0.8 | 0.7 | 0.6 | 0.5 | 0.6 |
| History of preterm birth | ||||||||||||||
| No | 84,156 | 97.0 | 97.1 | 96.8 | 96.3 | 95.8 | 96.7 | 83,518 | 97.0 | 96.9 | 97.0 | 96.6 | 96.4 | 96.6 |
| Yes | 2,934 | 3.1 | 3.0 | 3.2 | 3.7 | 4.2 | 3.3 | 2,799 | 3.1 | 3.1 | 3.0 | 3.4 | 3.7 | 3.4 |
| Infertility treatment | ||||||||||||||
| No | 81,311 | 92.8 | 92.0 | 92.7 | 94.1 | 95.8 | 96.4 | 80,638 | 93.3 | 91.7 | 92.7 | 93.7 | 95.2 | 95.9 |
| Ovulation stimulation/artificial insemination by sperm from husband | 3,158 | 3.9 | 4.4 | 3.9 | 3.4 | 2.5 | 2.1 | 3,109 | 3.8 | 4.4 | 3.9 | 3.5 | 2.8 | 2.5 |
| Assisted reproductive technology | 2,609 | 3.3 | 3.6 | 3.5 | 2.6 | 1.8 | 1.6 | 2,553 | 2.9 | 3.9 | 3.4 | 2.8 | 2.0 | 1.7 |
| Educational background, years | ||||||||||||||
| < 13 | 30,964 | 40.4 | 32.9 | 33.8 | 35.4 | 40.1 | 54.2 | 31,045 | 42.6 | 34.9 | 33.4 | 34.7 | 37.8 | 48.9 |
| ≥ 13 | 54,926 | 59.6 | 67.1 | 66.2 | 64.6 | 59.9 | 45.8 | 54,986 | 57.4 | 65.1 | 66.6 | 65.3 | 62.2 | 51.1 |
| Household income, million Japanese-yen/year | ||||||||||||||
| < 6 | 58,726 | 71.3 | 69.5 | 71.1 | 74.6 | 79.3 | 86.1 | 58,763 | 73.9 | 69.6 | 70.3 | 73.1 | 77.6 | 84.9 |
| ≥ 6 | 21,569 | 28.7 | 30.5 | 28.9 | 25.4 | 20.8 | 14.0 | 21,590 | 26.1 | 30.4 | 29.7 | 26.9 | 22.4 | 15.1 |
| Occupation in early pregnancy | ||||||||||||||
| Administrative, managerial, professional, and engineering workers | 20,047 | 22.0 | 26.3 | 25.5 | 22.9 | 17.1 | 9.7 | 19,798 | 20.2 | 24.7 | 25.7 | 24.4 | 19.6 | 12.9 |
| Clerical workers | 14,816 | 18.8 | 21.4 | 19.6 | 14.8 | 10.0 | 6.9 | 14,580 | 17.7 | 21.2 | 19.7 | 16.3 | 12.3 | 8.9 |
| Sales and service workers | 19,105 | 25.0 | 20.7 | 20.2 | 22.6 | 24.2 | 30.4 | 18,858 | 25.4 | 20.3 | 20.3 | 22.0 | 24.0 | 28.9 |
| Homemaker | 24,024 | 22.3 | 22.0 | 25.3 | 30.6 | 38.8 | 39.8 | 23,688 | 24.2 | 23.8 | 25.1 | 28.2 | 34.5 | 36.1 |
| Others | 8,472 | 11.8 | 9.6 | 9.4 | 9.2 | 9.9 | 13.2 | 8,360 | 12.5 | 10.1 | 9.2 | 9.2 | 9.6 | 13.2 |
| Type of delivery | ||||||||||||||
| Vaginal | 70,776 | 79.8 | 81.1 | 81.2 | 82.0 | 82.3 | 81.8 | 70,603 | 81.9 | 81.4 | 81.6 | 81.9 | 82.9 | 82.4 |
| Caesarean | 16,143 | 20.2 | 18.9 | 18.8 | 18.0 | 17.7 | 18.2 | 15,582 | 18.1 | 18.6 | 18.4 | 18.1 | 17.1 | 17.6 |
| Postpartum depressive symptoms at 1 month after delivery assessed by the Edinburgh Postnatal Depression Scale | ||||||||||||||
| Not depressive (score < 8) | 72,482 | 82.2 | 85.2 | 86.3 | 87.2 | 86.7 | 80.7 | 72,137 | 80.1 | 84.7 | 86.0 | 87.3 | 87.1 | 82.7 |
| Depressive (score ≥ 9) | 11,985 | 17.8 | 14.8 | 13.7 | 12.8 | 13.3 | 19.3 | 11,916 | 19.9 | 15.3 | 14.0 | 12.7 | 12.9 | 17.3 |
| Small for gestational age | ||||||||||||||
| No | 80,106 | 92.3 | 92.2 | 92.5 | 92.6 | 92.8 | 92.8 | 79,496 | 92.7 | 92.5 | 92.6 | 92.7 | 92.6 | 92.6 |
| Yes | 6,495 | 7.7 | 7.8 | 7.5 | 7.4 | 7.2 | 7.3 | 6,339 | 7.3 | 7.5 | 7.4 | 7.3 | 7.4 | 7.4 |
| Infant sex | ||||||||||||||
| Boys | 44,592 | 51.1 | 51.0 | 51.0 | 51.4 | 51.6 | 51.6 | 44,161 | 51.1 | 51.1 | 50.9 | 50.9 | 52.4 | 50.9 |
| Girls | 42,510 | 48.9 | 49.0 | 49.0 | 48.6 | 48.5 | 48.4 | 42,194 | 48.9 | 48.9 | 49.1 | 49.1 | 47.6 | 49.1 |
aSubgroup totals do not equal the overall number because of missing data.