Table 1.
Distribution of background characteristics in each analysis sample
| Characteristics | Age at menarche in years (n=8984) | Age at menopause in years (n=945) | Length of reproductive lifespan in years (n=841) |
| Age at delivery/enrolment | 28.5 (4.8) | 34.2 (3.4) | 34.2 (3.4) |
| Ethnicity | |||
| White/European | 8798 (97.9) | 927 (98.1) | 823 (97.9) |
| Other | 186 (2.1) | 18 (1.9) | 18 (2.1) |
| Educational qualifications | |||
| A level or above | 3499 (39.0) | 555 (58.7) | 495 (58.9) |
| O level or below | 5485 (61.0) | 390 (41.3) | 346 (41.1) |
| Parental highest educational qualifications | |||
| A level or above | 1784 (19.9) | 232 (24.6) | 210 (25.0) |
| O level or below | 4666 (51.9) | 489 (51.7) | 432 (51.4) |
| Missing | 2534 (28.2) | 224 (23.7) | 199 (23.7) |
| Paternal occupation | |||
| Non-manual | 3505 (39.0) | 487 (51.5) | 429 (51.0) |
| Manual | 3806 (42.3) | 330 (35.0) | 296 (35.2) |
| Missing | 1673 (18.6) | 128 (13.5) | 116 (13.8) |