Table 1  Randomized placebo-controlled studies: 17-OHPC for the prevention of preterm birth in women with singleton pregnancy and prior preterm birth.

Author	Year	Number of patients (17α-OHPC vs. control)	Inclusion criteria	Type of gestagen	Dosage and interval	Period of administration (GW)	Number of centers	Primary outcome
GW: weeks of gestation, i. m.: intramuscular application, 17-OHPC: 17-hydroxyprogesterone caproate, PB: preterm birth, SPB: spontaneous preterm birth, a Compilation of neonatal deaths, grade 3 or 4 intraventricular hemorrhage, infant respiratory distress syndrome, bronchopulmonary dysplasia, necrotizing enterocolitis, confirmed sepsis.
Meis et al.	2003	310 vs. 153	prior SPB (singleton)	i. m. 17-OHPC	250 mg per week	16 – 20 to 36	19	PB < 37 GW
Ibrahim et al.	2010	25 vs. 25	prior SPB (singleton)	i. m. 17-OHPC	250 mg per week	2nd trimester to 36	1	GW at birth, PB < 37 GW
Blackwell et al.	2019	1130 vs. 578	prior SPB (singleton)	i. m. 17-OHPC	250 mg per week	16 – 20 to 36	93 (41 USA, 52 non-USA)	PB < 35 GW, composite neonatal morbidity and mortaility index a