Facebook Advertisements for Inexpensive Participant Recruitment Among Women in Early Pregnancy.

Facebook advertisements were used to recruit nulliparous women in the first 20 weeks of pregnancy for an online survey about their childbirth preferences. A campaign of ads was targeted to women, aged 18 to 44 years, residing in the United States. The ads were viewed 10,577,381 times by 7,248,985 unique Facebook users over 18 weeks in 2011. The ad campaign yielded 6,094 clicks by 5,963 unique users at a mean cost of $0.63 per click and a unique click-through rate of 0.08%. Of those who clicked through to the study site, 18% (n = 1,075) consented to participate. The participant pool was reduced to 344 women after application of strict eligibility criteria. Participants represented 43 states and the District of Columbia, their mean age was 20.9 years (Mdn = 19.0, SD = 4.0), and their mean weeks' gestation was 11.5 (SD = 5.8). The campaign cost was $3,821.81 or $11.11 per eligible participant.