Search strategy
We conducted a literature search strategy without language restriction. We updated the exhaustive searches of the previous Cochrane reviews9,10from the oldest search date reported in Brownfoot 20139(February 13, 2013) until October 2019, in PubMed MEDLINE, EMBASE, LILACS,  Cochrane Library, Clinical Trials.gov and the International Clinical Trials Registry Platform (ICTRP) for ongoing trials search. The MeSH search terms included premature birth, betamethasone, dexamethasone and glucocorticoids (Full search strategy in Appendix S1 ). We also searched references of included studies and contacted experts for additional evidence.