| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
[29] Progesterone, PV: Jarde A, Lutsiv O, Beyene J, McDonald SD. Vaginal progesterone, oral progesterone, 17-OHPC, cerclage, and pessary for preventing preterm birth in at-risk singleton pregnancies: an updated systematic review and network meta-analysis. BJOG 2019; 126: 556–567. https://www.ncbi.nlm.nih.gov/pubmed/30480871
Progesterone, PV: National Department of Health: Affordable Medicines, EDP-Adult Hospital level. Medicine Review: Progesterone, vaginal for prevention of preterm labour, October 2019. http://www.health.gov.za/