Fletcher 1971.

Methods	This RCT was conducted on the women living in London. Participants were ascribed at random to 2 treatment groups.
Participants	Pregnant women booked for antenatal clinic (n = 643).
Interventions	Group1: ferrous sulphate 200 mg (n = 322). Group 2: ferrous sulphate 200 mg + folic acid 5 mg (n = 321).
Outcomes	Pre‐eclampsia (n = 643), serum folate levels (n = 643).
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "the subjects were ascribed at random to two treatment groups by instructing each patient to take one tablet daily".
Allocation concealment (selection bias)	Unclear risk	The methods used for allocation concealment was not stated in the text.
Blinding (performance bias and detection bias) All outcomes	Unclear risk	The methods used for blinding was not stated in the text.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Number of exclusions and attritions (along with their reasons) were not reported.
Selective reporting (reporting bias)	Unclear risk	The study appears to be free of selective reporting.
Other bias	Unclear risk	No other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.