Study designs of evaluations included in the review
Randomised controlled trials (RCTs) and observational studies with a comparison group and at least 6 months' follow-up were eligible.
Specific interventions included in the review
Studies of oral estro-progestative contraceptives compared with an alternative contraceptive method or no method of contraception were eligible for inclusion. Data on progestogen-only contraceptives were excluded. The type and dose of OC was not standardised in any of the included studies.
Participants included in the review
Studies of women with gestational trophoblastic disease (GTD), defined as complete hydatidiform mole diagnosed by pathologic examination of ovular tissue and submitted to uterine evacuation, were eligible. The included studies were from developing countries as well as North America and the UK. The stage of disease in the women varied between the included studies.
Outcomes assessed in the review
Studies assessing the presence of post-molar gestational trophoblastic tumour (GTT) for which the diagnostic criteria were specified, or beta-hCG regression time (defined as the number of weeks from the uterine evacuation of GTD to regression to normal levels), were eligible. Studies stopped before the normalisation of beta-hCG were excluded. The included studies used varying definitions for GTT and in the majority of studies the criteria were broader than those recommended by the International Federation of Obstetricians and Gynaecologists (FIGO).
How were decisions on the relevance of primary studies made?
Two reviewers independently assessed all potentially relevant studies for inclusion. Any disagreements were resolved by consensus. The authors of the primary studies were contacted when insufficient information was reported to establish eligibility.