When obstetricians' advice was reinforced with voucher payments for not smoking, pregnant women attained much higher abstinence rates, a recent NIDA-funded clinical study found. In addition, the women who earned vouchers scored higher than a control group on two out of three measures of third-trimester fetal growth, a predictor of newborns' health. The pay-for-proof approach has helped patients addicted to smoking and other drugs in previous trials; it was adapted to motivate pregnant women and new mothers.
A Little Added Incentive
Dr. Stephen Higgins, Dr. Sarah Heil, and colleagues at the University of Vermont recruited 82 pregnant low-income smokers for a trial of voucher-based reinforcement therapy (VBRT). Originally developed to treat cocaine abuse, VBRT dispenses cash-value vouchers to patients when they meet objective criteria for treatment progress. The value of the voucher awarded mounts with each consecutive favorable test result but resets to the base amount if the patient fails to meet the assigned monitoring criterion. Patients exchange vouchers for retail goods of their choice.
"VBRT uses the same basic principle to treat dependence that's operative in producing dependence," explains Dr. Higgins, the developer of VBRT. "Whereas the rewarding effects of drugs reinforce drug use, the rewards in the intervention reinforce abstinence from drug use."
In the Vermont study, the women chose a day, shortly after their recruitment, to stop smoking. To enhance motivation during the difficult early days of quit attempts, the researchers scheduled monitoring appointments daily for the first week after each woman's quit date. At these appointments, the women exhaled into a machine that measured levels of carbon monoxide, a component of cigarette smoke, in their breath. The 42 women randomized to VBRT received a voucher worth $6.25 for their first carbon monoxide reading below 6 parts per million. Each successive time they met this criterion, the value of their voucher increased by $1.25. A control group of 40 received vouchers worth $15 for showing up for monitoring, regardless of the results. All women in both groups also received advice and encouragement to quit smoking from their obstetricians.
After the first week, the researchers changed the reward criterion. To earn vouchers, the VBRT women now needed to submit a urine sample containing less than 80 ng/ml of cotinine, a nicotine metabolite. This more exacting criterion required a longer duration of abstinence. The researchers also monitored the women only twice weekly and eventually reduced the visits to every other week. Each lengthening of the interval between monitoring sessions reduced opportunities for the women to earn vouchers and increased the relative importance of a session in terms of reward. After delivery, when women who quit smoking for their infants' sake might have been vulnerable to starting again, the monitoring interval was shortened to once a week for 4 weeks. From weeks 5 to 12 postpartum, the every-other-week monitoring schedule was resumed.
The women in the VBRT group maintained abstinence for 9.7 weeks of their pregnancy, on average, compared with 2.0 weeks in the control group. Forty-one percent of the VBRT women, but only 10 percent of the control group, were abstinent at their last assessment before giving birth. Twenty-four percent of women in the VBRT group sustained abstinence throughout the entire third trimester of pregnancy, compared with only 3 percent of women in the control group. The clinic's outlay for vouchers to the women in the VBRT group averaged $461 per participant and ranged from $0 to $1,180.
More Robust Fetal Growth
The researchers obtained ultrasound measurements in the 30th and 34th weeks of 57 women's pregnancies to ascertain whether VBRT also promoted fetal growth. While previous studies found correlations between smoking abstinence, greater fetal growth, and higher neonatal birth weight, experimental evidence of the relationship has been considered weak.
The ultrasound results showed greater fetal growth in the 29 women in the VBRT group, compared with the 28 women in the control group. "It's known that smoking retards fetal growth, but demonstrating that a treatment actually increases growth is pretty rare," says Dr. Higgins.
"These findings are quite exciting, providing promising preliminary evidence of an association between higher abstinence rates in the third trimester and greater fetal growth," says Debra Grossman of NIDA's Division of Clinical Neuroscience and Behavioral Research. "In addition to the health benefits observed, VBRT may also provide cost savings, given the high medical costs for infants associated with maternal smoking."
Although the success rate for this intervention was high relative to conventional therapies, Dr. Higgins notes that 59 percent of the women who received VBRT continued to smoke throughout their pregnancies. The researchers are currently testing whether offering greater rewards at the start of the intervention or making changes in the voucher schedule could help more women quit. "Based on what we know from our research and that of other researchers in the field, the amount of the reward for changing behavior matters a lot," says Dr. Heil.
Dr. Higgins notes that there is not likely to be a one-size-fits-all approach to quitting smoking during pregnancy. "We anticipate needing an array of interventions tailored to these women," he says.
The impressive increase in abstinence among women in the VBRT group during pregnancy dropped by 24 weeks postpartum: 8 percent remained abstinent, compared with 3 percent of the control group. However, an earlier study by these investigators using the same conditions showed a bigger disparity: 27 percent of women in the VBRT group remained abstinent at 24 weeks postpartum compared with none in the control group.
Although abstinence may have been short-lived, VBRT benefits were substantial, especially in terms of fetal health. "Even if the effects only lasted while the intervention was in place, that would be a good thing for these women and their babies," Dr. Higgins concludes.
Heil, S.H., et al. Effects of voucher-based incentives on abstinence from cigarette smoking and fetal growth among pregnant women. Addiction 103(6):1009-1018, 2008. [Abstract]
Higgins, S.T., Silverman, K., and Heil, S.H. Contingency Management in Substance Abuse Treatment. New York, NY: The Guilford Press, 2008.