Perspectives on the design and methodology of periconceptional nutrient supplementation trials

Periconceptional supplementation could extend the period over which maternal and fetal nutrition is improved,

but there are many challenges facing early-life intervention studies. Periconceptional trials differ from pregnancy

supplementation trials, not only because of the very early or pre-gestational timing of nutrient exposure but also

because they generate subsidiary information on participants who remain non-pregnant. The methodological

challenges are more complex although, if well designed, they provide opportunities to evaluate concurrent

hypotheses related to the health of non-pregnant women, especially nulliparous adolescents. This review examines

the framework of published and ongoing randomised trial designs. Four cohorts typically arise from the

periconceptional trial design — two of which are non-pregnant and two are pregnant — and this structure

provides assessment options related to pre-pregnant, maternal, pregnancy and fetal outcomes. Conceptually the

initial decision for single or micronutrient intervention is central — as is the choice of dosage and content — in

order to establish a comparative framework across trials, improve standardisation, and facilitate interpretation of

mechanistic hypotheses. Other trial features considered in the review include: measurement options for baseline

and outcome assessments; adherence to long-term supplementation; sample size considerations in relation to

duration of nutrient supplementation; cohort size for non-pregnant and pregnant cohorts as the latter is influenced

by parity selection; integrating qualitative studies and data management issues. Emphasis is given to low resource

settings where high infection rates and the possibility of nutrient-infection interactions may require appropriate

safety monitoring. The focus is on pragmatic issues that may help investigators planning a periconceptional trial.