Table 1.

Characteristic of included studies (Randomized controlled trials)

Extremely preterm birth (less than 28 weeks of gestation)
Study ID	Country	Study design	Sample size (groups)	Description of women/patients with preterm labour	Intervention (Description)	Comparison (Description)	Outcomes
Richter 2005 [23]	Germany	Prospective-RT	40 (n = 20 vs. n = 20)	Women, 31–42 years of age, between 18 to 24th week of gestation and with uterine contractions duration >30 s, rate ≥ 4/30 min. Cervical effacement >50 % and cervical dilatation of 0–3 cm (nulliparous), and 1–3 cm (primiparous and multiparous)	Atosiban	Placebo	Prolongation of pregnancy >48 h
					(Initial intravenous infusion of 6.75 mg of atosiban in 0.9 ml of sodium chloride, and followed by high dosage of infusion (300 lg/ min) for 3 h and then low dosage (100 lg/min) up to 45 h.)	(Intravenous infusion of saline solution)	Prolongation of pregnancy >7 days
Romero 2000 [21]	USA	RCT	501 (n = 250 vs. n = 251)	Women between gestational age of 20 weeks to 33 weeks, with intact membranes, cervical dilatation of 1 to ≤3 cm, preterm labor required the presence of ≥4 uterine contractions over 30 min, each lasting at least 40 s.	Atosiban	Placebo	Prolongation of pregnancy >24 h
			77 a (n = 43 vs. n = 34)		(Initial intravenous infusion of 6.75 mg of atosiban over 1 min and followed by an infusion of 300 μg/min of atosiban for 3 h, and then 100 μg/min for up to 45 h.)	(Matching placebo contained same formulation minus the 5 % mannitol solution of atosiban.)	Prolongation of pregnancy >48 h
							Prolongation of pregnancy >7 days
							Perinatal death
The Canadian PLIG 1992 [22]	Canada	RCT	708 (n = 352 vs. n = 356)	Women between gestational age of 20 to 35 weeks, with uterine contractions four per 20 min or six per 60 min or any uterine activity with ether rupture membranes or cervical dilatation by 2 cm or more.	Ritodrine	Placebo	Perinatal death
			151 a (n = 76 vs. n = 75)		(Intravenous infusion of ritodrine in 5 % dextrose at a rate of 0.35 mg/min until the cessation of uterine activity, the failure of therapy, or occurrence of impermissible maternal side effects	(Dextrose solution alone without ritodrine)
Multiple gestations
No report found for tocolytic treatment for imminent risk of preterm labor
Growth-restricted fetuses
No report found for tocolytic treatment for imminent risk of preterm labor

^aSubset of < 28 weeks of gestation sample size extracted from total participant in the study; (n = intervention group vs. n = comparison group); perspective-RT, prospective randomized trial