Methods

All women delivering babies at six participating Portland, Oregon, metropolitan area hospitals received an in-hospital screening and were deemed eligible for the study if they reported smoking during the 30 days before the pregnancy and quitting during pregnancy, and were willing to speak with a Visiting Nurse Association (VNA) nurse about having quit smoking. Women were not eligible to be screened if there was a maternal or child illness that would prevent them from attending the paediatric well-baby visits; if the baby was being adopted; or if the woman did not speak English.

When an eligible woman agreed to participate in the study, the delivery nurse or the birth certificate clerk contacted the VNA. A VNA nurse informed the woman about the study, obtained informed consent, collected a saliva sample for cotinine verification of non-smoking status, and conducted the baseline assessment interview, preferably while the participant was still in the hospital. However, because of short postpartum hospital stays, just over half of the participants were interviewed in the hospital. The average time to interview for those interviewed in the hospital was 1.5 days postpartum (range 0–8 days), while the interview took place an average of 8.9 days postpartum (range 2–28 days) for those seen after discharge.

The baseline interview took approximately 20–30 minutes. Upon completion of the interview, the participant was randomised into either a control or relapse prevention intervention group. Controls received no intervention from the VNA nurse, and standard care from their paediatric provider. Women in the intervention group received a 15–30 minute relapse prevention intervention from the VNA nurse which included counselling about reasons for maintaining cessation and help in developing a plan for doing so. At the two week, and two and four month well-baby visits with the paediatric provider they received reinforcement if they had done so and if not, given encouragement and a plan to try to quit again.

After the VNA intervention, the principal investigator (PI) called all of the paediatric providers who would be seeing participants in the intervention group. All of the 85 paediatric providers contacted in this manner agreed to participate in the study. During this initial call, the PI conveyed the maternal smoking history, explained the purpose of the study, and briefly discussed how to conduct relapse prevention in the context of well-baby care. For subsequent participants who would be seeing the same paediatric provider, a letter with the participant's and infant's names, and a reminder about the study was faxed from the PI to the paediatric provider. The call or letter from the PI was followed by a packet of information that included a letter to the provider, chart stickers, tips on relapse prevention, and written materials for the participant.

Of the 9390 women who delivered and were eligible to be screened during the 14 months of recruitment, 9140 (97 %) were successfully screened. Of the 1837 (20%) new mothers who reported smoking cigarettes 30 days before pregnancy, 638 (35%) reported to have quit smoking during their pregnancy or within 30 days of becoming pregnant. Only 287 (55%) of those eligible were enrolled in the study; 141 were randomised into the experimental group, 146 into the control group. The others either refused to participate (196), relapsed back to smoking before the baseline interview (27), or were otherwise unable to enroll for a variety of reasons (12). Two women were excluded from the study because their cotinine concentrations indicated recent smoking.

Baseline data were collected during a face to face interview at the time of initial enrolment in the study. A follow up telephone interview was conducted approximately six months postpartum. Four women were excluded from the study at follow up because they were moving out of the Portland metropolitan area or were in the military, and thus had no specific paediatric provider during the follow up period; two women were excluded because they were not keeping their babies; and four did not complete the follow up survey, yielding 277 who completed the study.

Baseline and follow up measures were analysed using logistic regression. The primary dependent variable was smoking status at follow up, defined as any smoking, even a puff, in the previous seven days. Independent variables of interest included group assignment (intervention or control), demographics (race, age, education, employment, children, living with partner), and smoking related variables (age first smoked, number daily cigarettes smoked before quitting, time until first cigarette of the day, partners', friends' and family members' smoking status, number smokers in the home, home smoking rules, family, friends, and co-workers support for not smoking, confidence to stay quit, and depressive symptoms).

Bivariate logistic regression was used to establish which independent variables would be tested in the multivariate model (cut off for inclusion p < 0.10). The final multivariate model was built with the variables that retained significant independent associations with relapse status (p < 0.05).

Correlation and contingency table analyses were used to investigate whether reports of doctor advice to quit and receipt of relapse prevention materials were greater for women in the experimental group.