Miller 1970.

Methods	Time frame and location: September 1967 to June 1968 in Iowa City, Iowa (USA) Limited detail about methods Sample size calculation and outcome of focus: no mention
Participants	General with N and source: 50 women delivering healthy term infants at city hospital. Inclusion criteria: desire to nurse for 3 months and use oral contraceptives while nursing Exclusion criteria: none specified
Interventions	Treatment: COC containing norethindrone 1 mg plus mestranol 80 μg daily for 21 days Comparison: identically‐labeled placebos for 21 days Timing: postpartum day 14; all received COC starting 6 weeks postpartum
Outcomes	Measures: lactation duration, milk volume production. Results presented in figures without actual numbers; graphic variations not identified. Assessments: 3 weeks, 5 weeks, and 3 months postpartum
Notes	‐‐‐
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not specified
Allocation concealment (selection bias)	Unclear risk	Not specified
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants and investigators blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	Loss to follow‐up: 1 in each arm; 1 discontinuation in placebo arm