Table 1. Characteristics of cases and controls in the CPRD data.
| Characteristic | Cases n = 9,498 | Controls n = 18,171 |
|---|---|---|
| Observation period, mean years (SD) | 7.3 (4.6) | 7.3 (4.6) |
| Age at index date, N (%) | ||
| 20–29 years | 174 (1.8) | 345 (1.9) |
| 30–39 years | 1,941 (20.4) | 3,844 (21.2) |
| 40–49 years | 7,383 (77.7) | 13,982 (76.9) |
| One or more hormonal contraceptive prescription, N (%) | 4,195 (44.1) | 7,092 (39.0) |
| Number of recorded births, N (%) | ||
| No recorded births | 4,039 (42.5) | 7,708 (42.4) |
| 1–2 births | 4,493 (47.3) | 8,262 (45.5) |
| 3+ births | 996 (10.2) | 2,201 (12.1) |
| Time since last recorded birth (years)a, N (%) | ||
| < 5 years | 897 (9.4) | 1,357 (7.5) |
| 5–10 years | 713 (7.5) | 1,064 (5.9) |
| No birth recorded in the last 10 years | 7,888 (83.0) | 15,750 (86.7) |
| BMI [kg/m2]b, N (%) | ||
| <25 | 3,955 (52.5) | 6,604 (47.9) |
| 25+ | 3,579 (47.5) | 7,171 (52.1) |
| Alcohol intakeb, N (%) | ||
| Nondrinker and past drinker | 1,156 (16.7) | 2,050 (16.9) |
| Drinker | 5,772 (83.3) | 10,088 (83.1) |
| Tubal ligation, N (%) | 478 (5.0) | 965 (5.3) |
| Hysterectomy, N (%) | 331 (3.5) | 622 (3.4) |
| Bilateral oophorectomy, N (%) | 36 (0.4) | 79 (0.4) |
aBirths during the observation period only.
bPercentages for alcohol intake and BMI are expressed as proportions of women with known values only. 23.0% of women had missing BMI (20.7% cases, 24.2% controls). 31.1% of women had missing data on alcohol consumption (27.0% cases, 33.2% controls).
BMI, body mass index; CPRD, Clinical Practice Research Datalink; SD, standard deviation.