Reijnders 1988.

Methods	Unit of randomization: pregnancy Method of randomization: sequentially‐coded ampules supplied by the drug company Timing of randomization: 6‐7 weeks' gestation Blinding: yes (double) Number of centers: not stated Power calculation: yes (80% with 40 in each group) 64 women randomized, 0 women excluded, 64 women analyzed Source of funding: Schering
Participants	Women who fell into ≥ 1 of the following criteria: pregnancy after ovulation induction ≥ 2 previous miscarriages period of infertility for > 12 months Evidence of a viable fetus at 6 weeks of pregnancy was required to be enrolled in the trial Age: not stated Location: Netherlands Timing and duration: not stated
Interventions	500 mg/week IM of hydroxyprogesterone caproate Control: placebo Duration: from 7 weeks' gestation to 12 weeks' gestation
Outcomes	Miscarriage Preterm delivery
Notes	Impossible to tell which were results for the women with recurrent pregnancy loss Dates of study: not stated Funding sources: Schering Nederland BV for providing 17‐OHP‐C and for financial support Declarations of interest: not stated
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not stated
Allocation concealment (selection bias)	Low risk	Sequentially coded ampules supplied by central location
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blinded
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Not specifically stated but likely blinded and unlikely that knowledge of assignment would influence outcomes
Incomplete outcome data (attrition bias) All outcomes	Low risk	None
Selective reporting (reporting bias)	Low risk	None
Other bias	Low risk	None