Arikan 2011.

Methods	2‐arm RCT of IV ritodrine plus vaginal progesterone vs IV ritodrine alone.
Participants	83 women randomised in a hospital in Turkey ‐ 40 women to the control group and 43 to the experimental group. Inclusion criteria: singleton pregnancy between 24 and 34 weeks; admitted with threatened preterm labour (persistent contractions (> 6 in a 30‐minute period) with cervical dilation or effacement); intact membranes, cervical dilatation 2 cm or less, with no previous cervical cerclage. Exclusion criteria: chorioamnionitis, evidence of deteriorating maternal or fetal condition, history of cervical surgery, uterine anomaly, fetal anomaly.
Interventions	All women were hydrated with 500 mL of Ringers lactate over 30 minutes and then all received a ritodrine infusion adjusted every 20 minutes from 10 to 70 mL/hr (maximum 0.35 mg/min) until the cessation of uterine contractions, the failure of therapy (not clear within what time period) or the occurrence of unacceptable side effects including tachycardia, hypotension or chest pain. The therapy was continued for 6 hrs after the cessation of contractions. All women also received a single course of betamethasone (2 x 12 mg injections during the first 24 hrs after admission) Experimental intervention: together with the ritodrine infusion, women in the experimental group also received vaginal micronized natural progesterone 200 mg. After ritodrine was discontinued women continues to receive micronized progesterone until 37 weeks’ gestation (frequency of 200 mg doses not clear) (43 women) (i.e. progesterone used for both tocolysis and maintenance therapy). The control group received the ritodrine therapy only (40 women).
Outcomes	Time to delivery (latency period), gestational age at delivery, delivery before 37 weeks, infant birthweight, umbilical cord pH, Apgar score and perinatal mortality and morbidity, admission to NICU, RDS, confirmed sepsis.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated list.
Allocation concealment (selection bias)	Unclear risk	Not described.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Stated that a convincing placebo was not feasible and blinding was not attempted.
Blinding of outcome assessment (detection bias) All outcomes	High risk	Outcome assessors were not blinded.
Incomplete outcome data (attrition bias) All outcomes	Low risk	83 women were randomised and it was reported that none were lost to follow‐up.
Selective reporting (reporting bias)	Unclear risk	Assessment from published study report.
Other bias	Low risk	Reported that groups were comparable at baseline.