| 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 |
[17] Folic acid, oral: Royal College of Obstetricians & Gynaecologists. Green-top Guideline No. 68: Epilepsy in pregnancy, June 2016. https://www.rcog.org.uk/en/guidelines-research-services/guidelines/gtg68/