Table 1.
Characteristics of current users and non-users of combined oral contraceptives and adjusted relative risk of venous thromboembolism according to age, calendar year, and length of education
| Characteristics | Current users | Non-users | Adjusted rate ratio† (95% CI) | P value | |||||
|---|---|---|---|---|---|---|---|---|---|
| Women years | No of events* | Incidence per 10 000 exposure years | Women years | No of events* | Incidence per 10 000 exposure years | ||||
| Age (years): | |||||||||
| 15-19 | 571 333 | 239 | 4.2 | 670 766 | 49 | 0.7 | 1 (reference) | — | |
| 20-24 | 713 623 | 343 | 4.8 | 346 614 | 74 | 2.1 | 1.32 (1.13 to 1.54) | <0.001 | |
| 25-29 | 549 862 | 375 | 6.8 | 463 810 | 134 | 2.9 | 1.99 (1.66 to 2.38) | <0.001 | |
| 30-34 | 430 272 | 375 | 8.7 | 667 937 | 211 | 3.2 | 2.91 (2.40 to 3.55) | <0.001 | |
| 35-39 | 369 859 | 447 | 12.1 | 861 442 | 304 | 3.5 | 4.01 (3.31 to 4.87) | <0.001 | |
| 40-44 | 261 464 | 397 | 15.2 | 965 951 | 467 | 4.8 | 5.29 (4.36 to 6.41) | <0.001 | |
| 45-49 | 153 147 | 319 | 20.8 | 984 209 | 573 | 5.8 | 6.58 (5.43 to 7.99) | <0.001 | |
| Year: | |||||||||
| 2001 | 335 482 | 241 | 7.2 | 625 168 | 175 | 2.8 | 0.71 (0.62 to 0.81) | <0.001 | |
| 2002 | 339 078 | 251 | 7.4 | 601 282 | 198 | 3.3 | 0.76 (0.66 to 0.86) | <0.001 | |
| 2003 | 340 575 | 238 | 7.0 | 579 767 | 174 | 3.0 | 0.70 (0.61 to 0.80) | <0.001 | |
| 2004 | 342 354 | 276 | 8.1 | 562 409 | 205 | 3.6 | 0.81 (0.72 to 0.93) | 0.002 | |
| 2005 | 341 273 | 275 | 8.1 | 544 028 | 217 | 4.0 | 0.86 (0.76 to 0.97) | 0.02 | |
| 2006 | 339 578 | 293 | 8.6 | 529 811 | 205 | 3.9 | 0.87 (0.77 to 0.99) | 0.03 | |
| 2007 | 337 072 | 311 | 9.2 | 516 775 | 245 | 4.7 | 1.01 (0.90 to 1.15) | 0.82 | |
| 2008 | 336 606 | 287 | 8.5 | 508 635 | 190 | 3.7 | 0.90 (0.79 to 1.02) | 0.10 | |
| 2009 | 337 542 | 323 | 9.6 | 492 855 | 203 | 4.1 | 1 (reference) | — | |
| Level of education: | |||||||||
| Elementary school‡ | 695 339 | 762 | 11.0 | 1 194 278 | 748 | 6.3 | 1 (reference) | — | |
| High school§ | 365 466 | 275 | 7.5 | 505 821 | 125 | 2.5 | 0.60 (0.54 to 0.67) | <0.001 | |
| High school and middle education¶ | 576 803 | 673 | 11.7 | 1 295 503 | 518 | 4.0 | 0.68 (0.63 to 0.73) | <0.001 | |
| High school and long education** | 241 662 | 223 | 9.2 | 909 249 | 257 | 2.8 | 0.49 (0.44 to 0.55) | <0.001 | |
| No available information | 1 170 290 | 562 | 4.8 | 1 055 878 | 164 | 1.6 | 0.78 (0.68 to 0.90) | 0.0005 | |
*Events are venous thromboembolisms.
†Age estimates adjusted for year, level of education, and use of oral contraceptives; year estimates adjusted for age, level of education, and use of combined oral contraceptives; and education estimates adjusted for age, year, and use of combined oral contraceptives.
‡9-10 years of education.
§2-3 years of education after elementary school.
¶3-4 years of education after high school.
**5-6 years of education after high school.