Outcomes
PRETERM BIRTH, SECONDARY
The primary outcome (for the RCT only) was survey response rate, compared across the paper and push-to-web surveys. The response rates were calculated by dividing the total number of responses (excluding refusals, duplicate and unusable returns) by the total number of women sampled (excluding packs confirmed as undelivered). Separate postal and online response rates were also calculated for the paper and push-to-web surveys.The secondary outcomes were: respondent sociodemographic characteristics (age, ethnicity, country of birth, IMD, region of residence, cohabiting status (e.g. living with partner), education, parity and multiplicity); prevalence of key maternity indicators (homebirth, preterm birth, low birthweight, caesarean section); and financial cost (total cost and cost per respondent). These secondary outcomes were compared across the paper, push-to-web and social media surveys (only women living in England in the social media survey). All outcomes were assessed when data collection closed, which was the end of February in the social media survey and the end of March in the paper and push-to-web surveys.