Effects of voucher-based incentives on abstinence from cigarette smoking and fetal growth among pregnant women

Abstract

Aims: This study examined whether voucher-based reinforcement therapy (VBRT) contingent upon smoking abstinence during pregnancy is an effective method for decreasing maternal smoking during pregnancy and improving fetal growth.

Design, setting and participants: A two-condition, parallel-groups, randomized controlled trial was conducted in a university-based research clinic. A total of 82 smokers entering prenatal care participated in the trial.

Intervention: Participants were assigned randomly to either contingent or non-contingent voucher conditions. Vouchers exchangeable for retail items were available during pregnancy and for 12 weeks postpartum. In the contingent condition, vouchers were earned for biochemically verified smoking abstinence; in the non-contingent condition, vouchers were earned independent of smoking status.

Measurements: Smoking outcomes were evaluated using urine-toxicology testing and self-report. Fetal growth outcomes were evaluated using serial ultrasound examinations performed during the third trimester.

Findings: Contingent vouchers significantly increased point-prevalence abstinence at the end-of-pregnancy (41% versus 10%) and at the 12-week postpartum assessment (24% versus 3%). Serial ultrasound examinations indicated significantly greater growth in terms of estimated fetal weight, femur length and abdominal circumference in the contingent compared to the non-contingent conditions.

Conclusions: These results provide further evidence that VBRT has a substantive contribution to make to efforts to decrease maternal smoking during pregnancy and provide new evidence of positive effects on fetal health.

Figure 1

Point-prevalence abstinence at the end of pregnancy, 12, and 24 weeks postpartum. Women in the contingent condition (n=37) received voucher-based reinforcement therapy contingent on biochemically-verified smoking abstinence, and those in the non-contingent condition (n=40), received vouchers independent of smoking status. * indicates a significant difference between conditions (p < .05).

Figure 2

Mean (±SEM) weeks of continuous abstinence antepartum (top panel) and percentage of participants abstinent throughout the third trimester (bottom panel) in the contingent and non-contingent conditions. See Figure 1 for description of conditions. * indicates a significant difference between conditions (p < .05).

Figure 3

Mean (±SEM) rates of growth in estimated fetal weight (top panel), fetal femur length (bottom left panel), and fetal abdominal circumference (bottom right panel) between ultrasound assessments conducted during the third trimester. See Figure 1 for description of conditions. * indicates a significant difference between conditions (p < .05).