Table 7.
Incidence rates per 10,000 person-years and incidence rate ratios of venous thrombosis within all starters vs all switchers of combined oral contraceptives by follow-up duration in Denmark.
| N of starters | N of VT events among starters | Person-years among starters | IR of VT (per 10,000 person-years) in starters (95% CI) |
N of switchers | N of VT events among switchers | Person-years among switchers | IR of VT (per 10,000 person-years) in switchers (95% CI) |
IRR (95% CI) among switchers vs starters (ref.) | aIRRa (95% CI) among switchers vs starters (ref.) | |
|---|---|---|---|---|---|---|---|---|---|---|
| Follow-up duration | ||||||||||
| 1-3 | 855,617 | 273 | 205,174.78 | 13.31 (11.73-14.88) | 82,929 | 33 | 19,782.98 | 16.68 (10.99-22.37) | 1.25 (0.87-1.80) | 1.50 (1.04-2.16) |
| 4-6 | 569,599 | 181 | 133,920.87 | 13.52 (11.55-15.48) | 59,453 | 10 | 13,735.51 | 7.28 (2.77-11.79) | 0.54 (0.28-1.02) | 0.59 (0.31-1.10) |
| 7-9 | 469,344 | 102 | 108,615.89 | 9.39 (7.57-11.21) | 47,752 | 8 | 10,989.85 | 7.28 (2.24-12.32) | 0.78 (0.38-1.59) | 0.84 (0.41-1.74) |
| 10-12 | 393,303 | 66 | 91,349.75 | 7.22 (5.48-8.97) | 39,527 | 10 | 9068.20 | 11.03 (4.19-17.86) | 1.53 (0.78-2.97) | 1.55 (0.79-3.03) |
aIRR, adjusted incidence rate ratio; IR, incidence rate; IRR, incidence rate ratio; N, number; VT, venous thrombosis; Ref., reference.
a
Adjusted for age, obesity, and type of combined oral contraceptives.