Heikkilä 1982.

Methods	Time frame and location: no time frame; conducted in Helsinki, Finland Some methods from secondary article Sample size calculation and outcome of focus: not specified
Participants	General with N and source: 80 women, delivered at State Maternity Hospital Inclusion criteria: breastfeeding and amenorrheic Exclusion criteria: not specified
Interventions	Treatment: levonorgestrel‐releasing IUD (30 μg) Comparison: Nova T intrauterine device (IUD) (copper releasing) Timing: inserted 6 weeks postpartum; range 29 to 56 days in one report, and 32 to 56 days in another
Outcomes	Measures: breastfeeding duration (no sample sizes for analysis); infant growth measured outside of study and presented in figure without actual numbers Assessment: unclear source and time frame; 75 days after insertion for analysis of breastfeeding data; secondary report notes recording of bleeding and spotting on cards and clinic visits at 3, 6, 12 months
Notes	Third group was added later (not randomized); received levonorgestrel‐releasing IUD (10 μg)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Divided at random" into 2 groups
Allocation concealment (selection bias)	Unclear risk	Not specified
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Participants did not know which IUD they received (30 μg/day LNG‐IUD or Nova T).
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Loss to follow‐up: none Discontinuation (expulsion or removal): 4 LNG‐IUD 30 μg; 4 Nova T. Also, 2 excluded from study due to uterine perforation at insertion (group not specified). Sample sizes for analysis not specified or inconsistent across reports.