| Methods |
'Retrospective cohort' of women who were UK residents attending 1 fertility clinic and who had received at least 1 cycle of fertility treatment from 1975 to 1989. Identified from clinic records. Linked to National Health Service Central Register in England and Wales |
| Participants |
N = 5556; age 20 years or more at the time of treatment; resident in the UK; alive and cancer‐free from 1990. Exposed group (4188; 75%) received drugs to stimulate ovulation; unexposed group did not receive drugs |
| Interventions |
Fertility treatment; number of cycles was reported but no dosage was mentioned. Fewer than 2 cycles ‐ 20 (0.5%) women, between 2 and 4 cycles ‐ 1246 (30%) women, between 5 and 9 cycles ‐ 1770 (42%) women, 10 or more cycles ‐ 1152 (28%) women. Follow‐up for women who received ovarian stimulation ‐ 32,986 person‐years at risk; for women with no ovarian stimulation 9753 person‐years at risk |
| Outcomes |
Ovarian cancer by histological diagnosis (see Table 3) |
| Notes |
Follow‐up from 1990 to 1997; 43,811 person‐years at risk |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| Selection bias |
Low risk |
All women attending a single centre with no history of ovarian cancer at the beginning of the study and with at least 1 ovary |
| Confounding |
Unclear risk |
Factors adjusted for age at first clinical visit, years of first clinical visit, parity, time since first treatment, and age at the end of follow‐up |
| Performance bias |
High risk |
Medical records; no blinding of assessors to exposure status |
| Detection bias |
High risk |
Cancer registry; no blinding of assessors to case status |
| Attrition bias |
High risk |
N = 74 women (451 person‐years) excluded as follow‐up was restricted to 1990 onwards rather than the date of first treatment. These women had died, emigrated, or were diagnosed with cancer before 1990. Follow‐up for women who received ovarian stimulation ‐ 32,986 person‐years at risk; for women with no ovarian stimulation 9753 person‐years at risk |
| Selective reporting (reporting bias) |
Low risk |
All fertility drugs investigated were reported |
