Cetingoz 2011.

Study characteristics
Methods	Randomised placebo‐controlled double‐blind study Department of Obstetrics and Gynecology, Istanbul, Turkey From December 2004 to February 2007
Participants	170 women recruited (n = 160 randomised): 84 allocated to intervention and 76 allocated to placebo. Inclusion criteria: high‐risk pregnant women: twin pregnancies; pregnancies with at least 1 spontaneous preterm birth; uterine malformation; randomisation at 24 weeks' gestation Exclusion criteria: not stated. 2 abortions, 7 deliveries between 20 ‐ 24 weeks and 1 woman with prophylactic cerclage were excluded
Interventions	Intervention group: micronised progesterone (100 mg) administered daily by vaginal suppository between 24 and 34 weeks of gestation Control/Comparison group: placebo (100 mg) administered daily by vaginal suppository between 24 and 34 weeks of gestation
Outcomes	Delivery < 37 weeks Delivery < 34 weeks Preterm labour admission NICU admission Neonatal death
Notes	Funding sources: not reported Declarations of interest: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated random‐number list ‐ “Patients were allocated according to randomised number table”.
Allocation concealment (selection bias)	Low risk	Random‐number list generated centrally by research hospital pharmacy
Blinding of participants and personnel (performance bias) All outcomes	Low risk	“The participating women, their caregivers, and the research personnel were unaware of the woman’s study‐group assignments.”
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Treatment assignment blinded until delivery of last pregnant woman
Incomplete outcome data (attrition bias) All outcomes	Low risk	160 women were randomised ‐ 10 lost during follow‐up, 6 from the placebo group and 4 from intervention group 150 women analysed.
Selective reporting (reporting bias)	High risk	Trial was not registered and no published protocol
Other bias	Low risk	Sample size calculation met. No baseline group differences. ITT analysis undertaken Ethics approval obtained