Giner Velazquez 1976.

Methods	Time frame and location: no time frame; Mexico Limited details about methods Sample size calculation and outcome of focus: no mention; small sample size limits power
Participants	General with N and source: 20 women selected immediately after birth Inclusion criteria: age 18 to 36 years; adequate health and nutrition during pregnancy Exclusion criteria: not specified
Interventions	Treatment: OC containing norethindrone 350 μg Comparison: placebo Timing: starting 48 hours postpartum
Outcomes	Measures: average milk production; biochemical composition of milk; infant weights; results primarily in figures without actual numbers Assessments: 14 days
Notes	Information from report translation
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Divided randomly (12 treatment and 8 control)
Allocation concealment (selection bias)	Unclear risk	Not specified
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double blind; no detail
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No mention of discontinuation, loss to follow‐up or exclusions