Completed eligibility screens and surveys from each recruitment platform were exported from Qualtrics to STATA v 14.2 (StataCorp, College Station, TX) for analysis. Descriptive statistics (mean and 95% CIs or proportions) were calculated for the completed sample by platform for the following measures: age, race, education, income, current smoking status (currently smoking in pregnancy or quit since beginning of this pregnancy), gestational age, and number of previous pregnancies. To analyze the descriptive statistics, we performed chi-square contingency test, analysis of variance, Kruskal-Wallis, and Fisher exact test. Cost data were compiled from invoices and receipts for subject payment and HIT management services (mTurk), gift cards (GiftBit for Reddit respondents), platform payments (Qualtrics Panel Data and Soapbox Sample), and Reddit ad purchases. Cost per completed survey was calculated as total costs per platform divided by number of completed, quality surveys. Eligibility yield was calculated by dividing the number of respondents who met the inclusion criteria by the number of total respondents per platform, whereas quality yield was calculated by dividing the number of quality surveys (number of completed surveys that pass the pregnancy screening, smoking screening, attention checks, quality checks, and email checks) by the total number of completed surveys per platform.