The study was performed in the city of Trondheim, the capitol city in middle Norway with 160 000 inhabitants and approximately 2100 deliveries per year. The city holds a University with 20 000 students and 4500 employees. In all, 28 of 35 general practices (90 general practitioners), all eight community based midwifes and all 20 maternity health centres in Trondheim agreed to participate in the PACT study.
Cohorts and subjects
Sequential birth cohorts were established to evaluate the intervention programme. From September 1st 2000 to May 30th 2002 all pregnant women who consulted their GPs or community based midwifes for pregnancy care were eligible to participate in the control cohort of the PACT study. Of some 3600 eligible pregnant women in Trondheim during this period, 1788 (50%) women were included and completed the pregnancy questionnaire (Q1), and 1023 (57%) of the participating women completed the questionnaire (Q2) six weeks after delivery (Figure 1). Participating women in the control cohort received common, nationwide recommended, advice on life-style, including smoking behaviour, following the routines each health-worker was familiar with at that time.
From June 1st 2002 to December 15th 2004 women were invited and included to the intervention cohort of the study. Of some 5200 pregnant women eligible to participate in the intervention cohort during this period, 2051 (40%) women gave their consent and answered the pregnancy questionnaire, and 1109 (54%) of the participating women completed the questionnaire six weeks after delivery.
All pregnant women were eligible to the PACT study if they were able to understand and fill in a questionnaire in Norwegian language with no other inclusion or exclusion criteria for either cohort.
Intervention programme
The intervention programme on diet, indoor dampness, and smoking cessation was developed in collaboration with midwives, maternity care nurses, GPs, and parents as a multiple health behaviour intervention. The smoking intervention programme was a brief office intervention [14]. The intervention was adapted from the United States Department of Health and Human Services Public Health Service (USHPS) guideline "Treating Tobacco Use and Dependence. Clinical Practice Guideline"[15]. From June 2002 the intervention was adopted by the city health authorities to be implemented by all health professionals as an integrated part of the recommended maternity care life-style counselling programme in primary health care throughout Trondheim, regardless of participation in the PACT study or not. The intervention programme continued throughout pregnancy at GP and midwife consultations. The recommended primary care prenatal schedule for follow-up in Norway was the same for both cohorts and constitutes of 8–10 prenatal consultations with a GP or midwife from week 8–10 in pregnancy. This programme has been accessible to all women in Norway for many years, free of charge, and with an attendance rate of nearly 100%. The women were invited to bring their partners to the consultations, and if he was a smoker they were encouraged to make a smoking cessation effort together.
Midwifes, public health nurses and GPs were offered a three hours course to improve smoking cessation counselling skills, to obtain a consistent intervention and inspire enthusiasm [16]. All midwifes and 22 of the 28 participating group practices attended the course. In addition, all participating midwifes and GPs were supplied with written strategy guidelines describing the intervention in detail. Some 7% of the participating women in the intervention cohort were included by GPs that did not attend the three hours course. All women included in the intervention cohort were regarded as intervened upon whether their GP had delivered the intervention or not. Self-help materials to be offered to the participants were also distributed to all primary care health professionals. Continuous smoking cessation groups were allocated to the maternity care centres and administered by public health nurses. The health professionals received four follow-up newsletters during the intervention.
Outcome variables
PACT data
The primary outcome variable was self-reported parental smoking behaviour at six weeks postnatal. The participants were asked to complete a self-reported life-style questionnaire including smoking behaviour at the first maternity clinic check-up (gestational week 8–12) and later at six weeks after delivery. Parental smoking during pregnancy was assessed with two questions at the antenatal questionnaire. The women were asked if they or their partner were smoking at the beginning of pregnancy, if they were smoking now and daily and/or weekly cigarette consumption. A separate question was asked about the total numbers of cigarettes smoked indoors. The same questions were asked six weeks postnatal. Smoking was coded as a dichotomous variable, if they were smoking more than one cigarette a week they were coded as smokers, if the answer was "no" they were coded as non-smokers, and if the answers to all questions on smoking were missing they were coded as missing. No biomarker such as hair nicotine was measured.
National data
Aggregated data from the Medical Birth Registry of Norway (MBR) were used to illustrate smoking cessation in Norway and the two comparable cities of Bergen and Trondheim from 1999 to 2004.
Bergen is the second largest city in Norway, with 245 000 inhabitants and around 3200 deliveries per year, with a University with some 16 000 students. Smoking data from the MBR were available from 1999–2004. These data are collected as a mandatory procedure at discharge from any maternity ward in Norway. Forms are completed by a midwife or physician interview and by using the hospital medical records. The women are asked if they smoked at the beginning or end of pregnancy, and they can answer "no", "occasionally" and "yes". Smoking was coded as a dichotomous variable, "occasionally" and "yes" were coded as smokers,"no" as non-smokers. Data were available for approximately 90% of the women who gave birth during the period from 1999 to 2004 according to information from the MBR.
The non-responder study
To investigate if there was a selection bias among participants in the PACT study we conducted an non-responder study where 391 parents who consecutively visited maternal postnatal care were asked to complete a short and anonymous questionnaire on age, socioeconomics, allergic disease and smoking behaviour, regardless of participation in the PACT-study or not.
Educational data
Maternal and paternal education was not accounted for in the original questionnaire. Thus, some 800 randomly selected parents answered questions on education (797 women and 812 men), either written or by telephone interview.
Approvals
The Regional Committee for Medical Research Ethics for Central Norway approved the study (Ref 120–2000). The study was granted license by the Norwegian Data Inspectorate to process personal health data and one of the parents signed a written informed consent formula (Ref 2003/953-3 KBE/-).
Statistics
SPSS for Windows® ver.14.0 (Chicago, Ill. USA) was used for all statistical analyses. Comparisons between groups were tested by chi square tests for categorical data and independent t-tests for continuous data. Confidence intervals (95% CI) were estimated for prevalence and odds ratio using binomial distribution for dichotomous data, and normal distribution for continuous data. Confounding factors were identified by a priori knowledge, and maternal age at the beginning of pregnancy, parity; marital status, homeowner (as a proxy for social status) and paternal smoking at the beginning of pregnancy were tested in several models. The resulting set of covariates included maternal age at the beginning of pregnancy, parity and marital status. We used GLM with binomial regression in a predictive model (STATA ver. 10.0) to adjust smoking prevalence at the beginning of pregnancy, at inclusion and at 6 weeks post partum in both cohorts. Parental smoking was stratified into smokers and non-smokers at the beginning of pregnancy and at time of inclusion, and binary logistic regression models were used to estimate adjusted odds ratio (aOR) for smoking at inclusion and at six weeks postnatal, respectively, in the intervention cohort compared to the control cohort. Finally, binary logistic regression models were used to estimate aORs for the associations between smoking cessation before inclusion (spontaneous quitting) and background factors The results are analysed and presented according to the STROBE recommendations [17].