Table 1.
Characteristics of the study population
| Total | Infertility treatment | P | |||||||
| Natural conception | OI/AIH | ART | |||||||
| n=9655 | % | n=8895 | % | n=273 | % | n=487 | % | ||
| Mother’s age, mean (SD), years | 32.7 | 4.7 | 32.4 | 4.6 | 34.3 | 3.9 | 37.2 | 3.8 | <0.0001 |
| Pre-pregnancy BMI (kg/m2) | |||||||||
| <18.5 | 1365 | 14.1 | 1279 | 14.4 | 36 | 13.2 | 50 | 10.3 | 0.0707 |
| 18.5 to <25.0 | 7204 | 74.6 | 6636 | 74.6 | 196 | 72.1 | 372 | 76.3 | |
| ≧ 25.0 | 1083 | 11.2 | 977 | 11.0 | 41 | 15.0 | 65 | 13.4 | |
| Educational level | |||||||||
| High school graduate or less | 2711 | 28.1 | 2565 | 28.8 | 49 | 18.0 | 97 | 19.9 | <0.0001 |
| Junior or vocational college graduate | 3513 | 36.4 | 3215 | 36.1 | 100 | 36.6 | 198 | 40.7 | |
| University graduate or above | 2722 | 28.2 | 2457 | 27.6 | 102 | 37.4 | 163 | 33.5 | |
| Household income (JPY/year) | |||||||||
| <4 000 000 | 3117 | 32.3 | 2974 | 33.4 | 63 | 23.1 | 80 | 16.4 | <0.0001 |
| 4 000 000 to <6 000 000 | 3063 | 31.7 | 2810 | 31.6 | 86 | 31.5 | 167 | 34.3 | |
| ≥6 000 000 | 2992 | 31.0 | 2658 | 29.9 | 111 | 40.7 | 223 | 45.8 | |
| Cigarette smoking | |||||||||
| Never | 6194 | 64.6 | 5675 | 64.3 | 195 | 71.4 | 324 | 66.7 | <0.0001 |
| Stopped before pregnancy | 2291 | 23.9 | 2075 | 23.5 | 60 | 22.0 | 156 | 32.1 | |
| Stopped after pregnancy | 950 | 9.9 | 928 | 10.5 | 17 | 6.2 | 5 | 1.0 | |
| Smoked during early pregnancy | 152 | 1.6 | 150 | 1.7 | 1 | 0.4 | 1 | 0.2 | |
| Alcohol consumption | |||||||||
| Drinking at early pregnancy | 1917 | 20.0 | 1766 | 20.0 | 57 | 21.0 | 94 | 19.3 | 0.5426 |
| Former | 3273 | 34.1 | 3023 | 34.2 | 93 | 34.2 | 157 | 32.3 | |
| Never | 3871 | 40.3 | 3568 | 40.4 | 105 | 38.6 | 198 | 40.7 | |
| Cannot drink because of constitution | 536 | 5.6 | 482 | 5.5 | 17 | 6.3 | 37 | 7.6 | |
| Parity | |||||||||
| Nullipara | 4564 | 47.3 | 4024 | 45.2 | 202 | 74.0 | 338 | 69.4 | <0.0001 |
| Multipara | 5091 | 52.7 | 4871 | 54.8 | 71 | 26.0 | 149 | 30.6 | |
| Child’s sex | |||||||||
| Male | 4958 | 51.4 | 4581 | 51.5 | 137 | 50.2 | 240 | 49.3 | 0.5874 |
| Female | 4697 | 48.7 | 4314 | 48.5 | 136 | 49.8 | 247 | 50.7 | |
| Gestational age (weeks) | |||||||||
| ≥37 | 9017 | 93.4 | 8338 | 93.7 | 245 | 89.7 | 434 | 89.1 | <0.0001 |
| 34 to <37 | 482 | 5.0 | 417 | 4.7 | 26 | 9.5 | 39 | 8.0 | |
| 29 to <34 | 113 | 1.2 | 98 | 1.1 | 2 | 0.7 | 13 | 2.7 | |
| <29 | 33 | 0.3 | 32 | 0.4 | 0 | 0.0 | 1 | 0.2 | |
| Birth weight (g) | |||||||||
| ≥2500 | 8689 | 90.0 | 8037 | 90.4 | 229 | 83.9 | 423 | 86.9 | 0.0004 |
| <2500 | 952 | 9.9 | 844 | 9.5 | 44 | 16.1 | 64 | 13.1 | |
| Birth defect | |||||||||
| No | 9477 | 98.3 | 8740 | 98.4 | 269 | 98.5 | 468 | 96.1 | 0.0033 |
| Yes | 169 | 1.8 | 146 | 1.6 | 4 | 1.5 | 19 | 3.9 | |
| Multiple birth | |||||||||
| No | 9440 | 97.8 | 8746 | 98.3 | 244 | 89.4 | 450 | 92.4 | <0.0001 |
| Yes | 215 | 2.2 | 149 | 1.7 | 29 | 10.6 | 37 | 7.6 | |
| ASQ-3 (2Y) | |||||||||
| >Mean −2SD | 8218 | 85.1 | 7626 | 85.7 | 215 | 78.8 | 377 | 77.4 | <0.0001 |
| ≤Mean −2SD | 1437 | 14.9 | 1269 | 14.3 | 58 | 21.3 | 110 | 22.6 | |
| ASQ-3 (3.5Y) | |||||||||
| >Mean −2SD | 8398 | 87.0 | 7746 | 87.1 | 233 | 85.4 | 419 | 86.0 | 0.5749 |
| ≤Mean −2SD | 1257 | 13.0 | 1149 | 12.9 | 40 | 14.7 | 68 | 14.0 | |
| Father’s age, mean (SD), y | n=4183 | n=3784 | n=142 | n=257 | |||||
| 34.5 | 5.7 | 34.2 | 5.6 | 35.1 | 4.8 | 38.8 | 5.2 | <0.0001 | |
AIH, artificial insemination with husband’s semen; ART, assisted reproductive technology; ASQ-3, Ages & Stages Questionnaires, Third Edition; BMI, body mass index; OI, ovulation induction.