Table 1.
Variables examined and data collection protocols
| Instrument | Operationalisation | Name of variables collected |
|---|---|---|
| Folic acid (FA) questionnaire | Self-reported supplement use Completed under the supervision of research dietitian | FA supplement information: |
| ∙ Preconceptional use∙ Postconceptional use∙ Timing of commencement∙ Compliance with supplementation∙ Brand of supplement used∙ Dose of FA taken | ||
| Sociodemographic questionnaire | Self-reported sociodemographic data Completed under the supervision of research dietitian | Sociodemographic information: |
| ∙ Place of birth∙ Years spent living in Ireland∙ Smoking status∙ Years of full-time education completed∙ Age finished full-time education∙ Relative income poverty∙ Relative deprivation∙ Consistent poverty | ||
| Tanita Body Composition Analyser, model MC-180MA III (Tanita Corp., Tokyo, Japan) | The woman was instructed to stand in bare feet on the electrode panel for measurement. Feet were positioned on the heel and toe electrodes on each side in roughly equal proportions. The woman was then instructed to take the handle electrodes in her hands and place the arms straight down during measurement. Contact between the arms and torso, and between the inner thighs, was avoided | Weight (kilograms) |
| Seca wall-mounted digital metre stick (Seca, Birmingham, UK) | The woman was instructed to stand straight and to stretch with her heels against the measuring rod. The woman’s head was placed in the Frankfort plane (top of the external ear canal and the lower bone of the eye socket in a horizontal plane parallel to the floor). The head plate was lowered until it touched the top of the head, compressing the hair. The woman was asked to inhale deeply and maintain a fully erect position, while maintaining the head in the Frankfort position. Height was recorded to the nearest 0·1 cm | Height (centimetres) |
| Computer medical system | The hospital’s computerised medical system was accessed to obtain additional patient details | ∙ Marital status∙ Parity∙ Planned pregnancy∙ Assisted reproduction∙ Booking gestation (weeks) |