Table 1.

Characteristics of the included studies (n = 9).

Study	Year	Study design	Eligibility criteria	Sample size	Interventions
Alimohamadi et al. [11].	2013	Randomized (double-blind)	Vaginal bleeding and uterine cramps before the 20th week of pregnancy, live singleton by ultrasound	71  71	Vaginal progesterone: 200 mg, twice a day for 1 week  Control: placebo using the same method
Czajkowski et al. [19].	2007	Randomized (double-blind)	Vaginal bleeding usually accompanied by abdominal pain before 12 weeks of pregnancy, live singleton by ultrasound	29  24	Vaginal progesterone: micronized, 300 mg, once per day for 6 weeksa  Oral dydrogesterone: 30 mg using the same method
El-Zibdeh and Yousef [12].	2009	Quasi-randomized (open-label)	Mild or moderate vaginal bleeding during the first trimester of pregnancy, live embryo by ultrasound	86  60	Oral dydrogesterone: 10 mg, twice per day until 1 week after bleeding had stopped  Control: conservative treatment
Gerhard et al. [13].	1987	Randomized (double-blind)	Vaginal bleeding during the first trimester of pregnancy, live singleton by ultrasound	17  17	Vaginal progesterone: 25 mg, twice per day for 14 days after bleeding had stopped  Control: placebo using the same method
Hui et al. [20].b	2015	Randomized	Vaginal bleeding between weeks 6 and 10 of pregnancy	41  42	Vaginal progesterone: micronized Oral dydrogesterone
Omar et al. [14].	2005	Randomized (open-label)	Mild or moderate vaginal bleeding before 13 weeks of pregnancy, live embryo by ultrasound	74  80	Oral dydrogesterone: initial: 40 mg; maintenance: 10 mg, twice per day until bleeding had stopped or for 1 weekc  Control: conservative treatment
Pandian [15].	2009	Randomized (open-label)	Vaginal bleeding up to the 16th week of pregnancy, live embryo by ultrasound	96  95	Oral dydrogesterone: initial: 40 mg; maintenance: 10 mg, twice per day until the 16th week of pregnancy  Control: conservative treatment
Palagiano et al. [16].	2004	Randomized (double-blind)	Vaginal bleeding and uterine cramps between weeks 6 and 12 of pregnancy with a previous diagnosis of inadequate luteal phase, live embryo by ultrasound	25  25	Vaginal progesterone: micronized, 90 mg, once per day for 5 daysd  Control: placebo using the same method
Yassaee et al. [17].	2014	Randomized (single-blind)	Vaginal bleeding until the 20th week of pregnancy, live singleton by ultrasound	30  30	Vaginal progesterone: micronized, 400 mg, once per day until bleeding stopped within less than 1 week Control: conservative treatmente

^aAdamed Inc., Poland; ^blimited information was available because the study was published only in abstract form; ^cunclear data regarding the duration of treatment; ^dCrinone 8%® (progesterone gel, Merck Serono Inc., Germany); ^eCyclogest® (Actavis Inc., UK).