Vessey 1998.

Methods	Cohort study in UK; Oxford‐Family Planning Association study Study began 1968; women followed until age 45 or 1994
Participants	17,032 women recruited at 17 large family clinics in England and Scotland, 1968 to 1974. Inclusion criteria: age 25 to 39 years; married; white and British; willing to cooperate; and either current OC user > 5 months or current user of diaphragm or intrauterine device of > 5 months without previous OC exposure
Interventions	Oral contraceptive use versus no OC use by age 45
Outcomes	First fracture Insufficient data for analysis; results presented as reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Case definition and representativeness	Unclear risk	Not applicable
Exposed cohort: representativeness	Low risk	Exposed cohort: OC used > 8 years or other duration by age 45 years (187,000 woman‐years for ever‐users; N not provided)
Control selection and definition; non‐exposed cohort selection	Low risk	Non‐exposed cohort: OC never used by age 45 years (123,000 woman‐years; N not provided)
Exposure ascertainment, including same method for cases and controls	Low risk	Interview by physician or nurse at clinic visits; included changes in contraceptive practices and reasons for changes Type of OC gathered, e.g., progestin‐only, or high or low estrogen content OC use analyzed by duration of use (months) and interval since last use (months); < 12, 13 to 24, 25 to 48, 49 to 72, 73 to 96, 97 to 120, > 121).
Outcome assessment (cohort study): method and evidence outcome not present at study start	Low risk	First referral to hospital for fracture (inpatient and outpatient), obtained in interview by physician or nurse at clinic follow‐up visits. Diagnoses on discharge confirmed by discharge letters, summaries, and pathology reports. Fractures presented for 3 most common types (radius or ulna, ankle, tarsals or metatarsals) and all fractures.
Comparability of groups on basis of design or analysis	Unclear risk	At age 45, OC use defined as (1) OC never used, (2) OC used > 8 years, and 3) other duration. First 2 groups followed annually until 1994. Group 3 excluded from study analysis from age 45 onward. Potential confounders examined in univariate analysis by type of fracture: age, parity, social class, smoking, height, weight, BMI. Association between fracture and age was significant (related to nearly all fracture types). For fractures of ankle and tarsals or metatarsals, weight and body mass index also significant. Analyses of association between fracture and OC use adjusted by age only.
Case‐control: non‐response rate	Unclear risk	Not applicable
Cohort: follow‐up length and adequacy (including loss to follow‐up)	Low risk	Women who stopped attending clinic were sent a postal version of follow‐up form; if not returned, women were interviewed by telephone or at home visit. Women followed annually until age 45 or 1994. Loss to follow‐up: 0.4% per year