Table 6.
Incidence rates per 10,000 person-years and incidence rate ratios of venous thrombosis within all switchers vs all starters of combined oral contraceptives by follow-up duration in the Netherlands.
| 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 | 9,851,084 | 739 | 1,204,535 | 6.14 (5.69-6.58) | 450,748 | 30 | 36,215 | 8.28 (5.32-11.25) | 1.35 (1.26-1.45) | 1.77 (1.22-2.56) |
| 4-6 | 11,494,639 | 547 | 910,875 | 6.01 (5.50-6.51) | 347,721 | 18 | 28,061 | 6.41 (3.45-9.38) | 1.07 (0.95-1.20) | 1.20 (0.74-1.93) |
| 7-9 | 8,360,085 | 423 | 666,169 | 6.35 (5.74-6.95) | 303,168 | 8 | 24,380 | 3.28 (1.01-5.56) | 0.52 (0.40-0.66) | 0.58 (0.29-1.17) |
| 10-12 | 7,013,938 | 296 | 579,853 | 5.10 (4.52-5.69) | 266,814 | 14 | 22,585 | 6.20 (2.95-9.45) | 1.21 (1.05-1.41) | 1.43 (0.83-2.48) |
aIRR, adjusted incidence rate ratio; IR, incidence rate; IRR, incidence rate ratio; N, number; VT, venous thrombosis; Ref., reference.
a
Adjusted for age and type of combined oral contraceptives.