Table 8.
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, restricted to age ≤30 years.
| 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 | 593,673 | 116 | 143,349.02 | 8.09 (6.62-9.56) | 64,034 | 15 | 15,322.72 | 9.79 (4.84 -14.74) | 1.21 (0.71-2.07) | 1.24 (0.72-2.14) |
| 4-6 | 431,958 | 102 | 101,996.87 | 10.00 (8.06-11.94) | 47,360 | 6 | 10,965.48 | 5.47 (1.09-9.85) | 0.55 (0.24-1.25) | 0.55 (0.24-1.24) |
| 7-9 | 363,258 | 65 | 84,518.76 | 7.69 (5.82-9.56) | 38,507 | ≤5 | Not reportable | 4.50 (0.09-8.90) | 0.58 (0.21-1.60) | 0.58 (0.21-1.60) |
| 10-12 | 308,808 | 35 | 72,070.71 | 4.86 (3.25-6.47) | 32,257 | 8 | 7426.37 | 10.77 (3.31-18.24) | 2.22 (1.03-4.78) | 2.17 (1.00-4.71) |
aIRR, adjusted incidence rate ratio; IR, incidence rate; IRR, incidence rate ratio; N, number; VT, venous thrombosis; Ref., reference.
a
Adjusted for obesity and type of combined oral contraceptives.