Basic characteristics of study participants (n=32 748)
| Number (percentage) | Mean±SD | Median | |
| Age, years | 28.6±8.6 | 28 | |
| 15–19 | 6141 (18.8) | ||
| 20–24 | 6118 (18.7) | ||
| 25–29 | 5825 (17.8) | ||
| 30–34 | 5483 (16.7) | ||
| 35–40 | 4687 (14.3) | ||
| 41–45 | 4494 (13.7) | ||
| Level of education | |||
| Low | 4020 (12.3) | ||
| Medium | 12 335 (37.9) | ||
| High | 16 229 (49.8) | ||
| Hours/week | |||
| Paid work | 21.7±14.7 | 24 | |
| Study | 7.4±13.6 | 0 | |
| Voluntary work | 0.8±3.1 | 0 | |
| Menstrual cycle | |||
| Regular cycle | 25 717 (78.5) | ||
| Duration | 28.8±3.0 | 28 | |
| Amenorrhoea due to LG-IUD/OC | 3675 (11.2) | ||
| Irregular, variation >10 days per cycle | 2495 (7.6) | ||
| Do not know | 861 (2.6) | ||
| Days with blood loss per cycle | 5.4±1.6 | 5 | |
| Visited a doctor for MRSs | |||
| No | 17 873 (54.6) | ||
| Yes, general practitioner | 10 141 (31.0) | ||
| Yes, gynaecologist | 4698 (14.4) | ||
| Diagnosis for MRSs* | |||
| No | 29 731 (90.8) | ||
| Yes | 3017 (9.2) | ||
| Endometriosis | 1120 (3.4) | ||
| PCOS | 588 (1.8) | ||
| Adenomyosis | 103 (0.3) | ||
| Fibroids | 275 (0.8) | ||
| Other | 1901 (5.8) | ||
| Contraception* | |||
| Hormonal contraception | 11 993 (36.6) | ||
| OC | 8650 (26.4) | ||
| LG-IUD | 2752 (8.4) | ||
| Other hormonal: injection, transdermal and so on | 882 (2.7) | ||
| No hormonal contraception | 20 755 (63.4) | ||
| Cu-IUD | 771 (2.4) | ||
| Female sterilisation | 423 (1.3) | ||
| No female contraception | 19 639 (60.0) | ||
| Nulliparous | 21 585 (66.0) | ||
| Paid work >5 hours a week | 26 104 (79.7) | ||
| Age | 29.7±8.3 | 29 | |
| Hours of paid work/week | 27.0±11.4 | 28 | |
| Hours spent on study/week | 7.5±13.4 | 0 | |
| >40 hours of paid work/week | 1047 (3.2) | ||
| Study >5 hours a week | 8764 (26.8) | ||
| Age | 22.0±6.2 | 20 | |
| Hours spent on study/week | 27.4±12.1 | 30 | |
| Hours of paid work/week | 15.5±11.3 | 12 | |
| >40 hours spent on study/week | 322 (1.0) |
Mean duration of cycle based on women with a regular cycle.
*More than one answer possible.
Cu-IUD, copper intrauterine device; LG-IUD, levonorgestrel-releasing intrauterine device; MRSs, menstruation-related symptoms; PCOS, polycystic ovary syndrome; OC, oral contraceptive.