Chanarin 1965.

Methods	The RCT was conducted on pregnant women coming to antenatal clinics at Saint Mary Hospital, London.
Participants	Pregnant women coming to antenatal clinic (n = 144).
Interventions	Women were allocated to 1 of the following 3 groups. Group 1: ferrous fumarate 100 mg (n = 50). Group 2: ferrous fumarate with 10 µg folic acid (n = 52). Group 3: lactose (n = 42). Subjects were asked to take 1 throughout pregnancy.
Outcomes	Mean urinary excretion (n = 144), mean haemoglobin (n = 144).
Notes	For this review, group 1 was compared with group 2.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "women were allocated at random to one of the three groups".
Allocation concealment (selection bias)	High risk	Insufficient information about allocation concealment.
Blinding (performance bias and detection bias) All outcomes	Low risk	Quote: "Glaxo Laboratories supplied these drugs with green, blue or red labels and the precise contents of each batch being unknown to us during the trials". Comment: investigators blinded, it seem from the available information that it was a single blinded study.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Insufficient information.
Selective reporting (reporting bias)	Unclear risk	Insufficient information.
Other bias	Unclear risk	No other bias identified but insufficient information available to fully assess this 'Risk of bias' domain.