Characteristics of included, excluded and ongoing studies
The included trials had heterogeneous characteristics and intervention schemes. The most common doses used were 24 mg of dexamethasone and betamethasone (Appendix S2 : Table S2.1 ,S2.2 ). The studies were published between 1972 and 2019. Sixteen studies were conducted in the USA, four in Iran, and two studies each were conducted in United Kingdom, the Netherlands, Finland, France, Israel and Brazil. Most studies were conducted in HICs (37), five in upper MICs and only three in lower MICs (median GNI per capita was 20,170 USD). The sample size varied from 18 to 2,831 women (median 118 women). Membranes were intact, ruptured and mixed (both intact and ruptured) in 7, 12 and 26 studies, respectively. Regarding the recruitment gestational age, 30 RCTs set 23-28 weeks as the lower limit and 33 studies set 34-37 weeks as the upper limit (median gestational age 30.44 weeks).
Table S2.3 describes the ongoing studies’ characteristics,6,77-79and Table S2.4 the reason of excluded studies initially included by full-text80-82).