TABLE 1.

Characteristics of included randomized trials

	Randomized trial
Characteristic	Ashoush et al, 201710	Glover et al, 201111	Rai et al, 200912
Methods	Double blind randomized controlled trial	Double blind randomized controlled trial	Double blind randomized controlled trial
Location	Egypt	United States	India
Sample size	205	33	148
Oral progesterone dose	100 mg every 6 hrs until 37 wks gestation (N=103)	400 mg twice daily until 34 wks gestation (N=19)	100 mg twice daily until 36 wks gestation (N=74)
Comparator	Placebo (N=102)	Placebo (N=14)	Placebo (N=74)
Gestational age range at randomization	14–18 Wks	16–20 Wks	18–24 Wks
Inclusion criteria	Singleton gestation 14–18 wks, previous spontaneous preterm birth at <37 wks gestation	Singleton gestation <20 wks, previous spontaneous preterm birth at 20–36 wks 6 d	Singleton gestation 18–24 wks, previous spontaneous preterm birth at 16–36 wks 6 d
Assessment of cervical length	Cervical length ultrasound scan at 20 wks gestation	Cervical length ultrasound scan at least once at <24 wks gestation, every 2 wks if cervical length was 10–25 mm, weekly for cervical length <10 mm	Cervical length assessment in second trimester
Management of short cervix	Cerclage offered for cervical length <15 mm	Cerclage offered for cervical length <5 mm	Not reported
Primary outcome	Preterm birth at <37 wks gestation	Preterm birth at <37 wks gestation	Mean prolongation of pregnancy