Participants
Figure 1 shows the flow diagram for participant selection. For baseline analysis, from the 348 couples who consented to participate, data from 286 couples who met the inclusion criteria were analysed. The included couples were randomly assigned to either the EG (140 couples) or CG (146 couples) using a central randomisation process. Three months post-intervention, 110 male partners and 109 pregnant women in the EG (21% dropout rate), and 104 couples in the CG (29% dropout rate), provided data for the primary and secondary outcomes. The final number of couples was 214 (EG: 110; CG: 104). Regarding reasons for dropouts, at three months post-intervention, most of these participants had moved to another place, while some couples could not visit the health facility. At this point, the trial was terminated due to COVID-19 restrictions.
Baseline participant characteristics
Independent sample t-tests were conducted, based on the assumptions of the central limit theorem[51], to identify significant differences in the demographic characteristics of the two groups. Table 1 shows the results for pregnant women and their partners. Most couples were of the Minahasan ethnicity, had completed high school, and were Protestants. SHS at home (EG: 82.1%; CG: 77.4%) was a daily occurrence for most of the women (EG: 75.7%; CG: 68.5%). The mean age of the pregnant women was 27.01 (SD = 6.4) in the EG and 26.89 (SD = 6.1) in the CG. The mean number of gestational weeks was 15.13 (SD = 6.7) in the EG and 15.00 (SD = 6.1) in the CG. The mean age of the male partners was 30.03 (SD = 6.9) in the EG and 30.22 (SD = 6.6) in the CG. The mean number of cigarettes male partners smoked per day was 10.28 (SD = 6.2) in the EG, and 10.75 (SD = 7.5) in the CG. Regarding the frequency of smoking at home, we recruited male partners who smoked at least six cigarettes per week, as per the inclusion criteria. Couple characteristics showed no between-group differences.
Primary outcome analyses for SHS avoidance in pregnant women
For pregnant women’s self-reported SHS avoidance, independent sample t-tests were conducted based on the assumptions of the central limit theorem[51] (Table 2, A1– A19). Overall, at baseline, there were no differences between groups, except for the following items: A16, ‘I routinely associate with people who smoke’ (t-test (df = 283) = -2.16, MD = -.2, 95% CI [-.37, .02], p-value = .031), and A17, ‘when eating out, I always sit in the non-smoking section’ (t-test (df = 282.3) = 2.07, MD = .20, 95% CI [.01, .38], p-value = .040).
Three months post-intervention, five items showed significant differences: A1, ‘when I encounter someone who is smoking, I distance myself to ensure that I am not exposed to the smoke’ (t-test (df = 210) = 2.09, MD = 0.19, 95% CI [.01, .37], p-value = .038); A6, ‘when I travel by bus, or any other public transportation I request a non-smoking seat’ (t-test (df = 210) = 2.44, MD = .24, 95% CI [.05, .43], p-value = .016); A12, ‘when at outdoor functions where smoking is present, I move away to avoid it’ (t-test (df = 185) = 2.90, MD = .25, 95% CI [.08, .41], p-value = .004); A13, ‘when at outdoor functions where water pipe smoking is present, I move away to avoid it’ (t-test (df =185) = 2.67, MD = .24, 95% CI [.06, .41] , p-value = .008); and A18, ‘I don't frequently visit places where smoking is prevalent’ (t-test (df = 184) = 2.28, MD = .21 95% CI [.03, .39], p-value = .024).
For male partners’ evaluation of their pregnant partners’ SHS avoidance, see Table 2. For B1–B3, there were no differences at baseline or three months post-intervention between groups.
Primary outcome analyses of male partners’ smoking behaviours
An independent samples t-test was conducted based on the assumptions of the central limit theorem[51], to assess differences in male partners’ self- and partner-reported smoking behaviours (Table 3, A1–A8). For self-reported smoking behaviours at baseline, there were no differences between groups, except for A1, ‘I read educational comics on preventing SHS at home’ (t-test (df = 273) = 3.23, MD = .42, 95% CI [.16, .67], p-value < .001). This difference remained statistically significant three months post-intervention. Three months post-intervention, there was a trend towards significance for A5, ‘I smoke outdoors with the door closed’ (t-test (df = 209) = 1.96, MD = .22, 95% CI [-.00, .43], p-value = .051). There was a significant difference between groups for A7, ‘I intend to quit smoking’ (t-test (df = 205) = 2.11, MD = .24, 95% CI [.02, .47], p-value = .035).
For male partners’ smoking behaviours as reported by pregnant women at baseline (Table 3, B1–B8), there were no significant differences between groups, except for B1, ‘male partner reads an educational comic on preventing SHS at home’ (t-test (df = 283) = 2.00, MD = .25, 95% CI [.00, -.51], p-value = .049). Three months post-intervention, there were differences between groups for the following four items: B1‘male partner reads an educational comic on preventing SHS at home’ (t-test (df = 208) = 4.13, MD = .62, 95% CI [.33, .92], p-value < .001); B2, ‘male partner moves away from me when he smokes’ (t-test (df = 205) = 2.11, MD = .24, 95% CI [.02, .46], p-value = .036); B4, ‘male partner smokes near the kitchen fan’ (t-test (df = 204) = 2.52, MD = .27, 95% CI [.06, .48], p-value = .012); B5, ‘male partner smokes outdoors with the door is closed’ (t-test (df =205) = 3.58, MD = .38, 95% CI [.17, .59], p-value < . 001); and B7, ‘male partner intends to quit smoking’ (t-test (df =205) = 2.72, MD = .30, 95% CI [.08, .51], p-value = .007).
Secondary outcome analyses of pregnant women’s health beliefs and self-efficacy
An independent samples t-test was conducted based on the assumptions of the central limit theorem[51], to assess differences in pregnant women’s health beliefs and self-efficacy (ST1). For most items, no significant differences were observed between groups at baseline or three months post-intervention. Three months post-intervention, the mean score of one self-efficacy item, I3, ‘it is easy for me to stick to my aims and accomplish my goals’, showed a significant between-group difference (t-test (df = 208) = .188, MD = .15, 95% CI [.01, .29], p-value = .032).
The cross-tabulation table (ST2) indicates pregnant women’s health beliefs and self-efficacy as evaluated by them at three months post-intervention. Three months post-intervention, almost all pregnant women (91.7~100%) in both groups selected the correct answers for all SHS knowledge questions. For perceived SHS-related disease susceptibility, almost all pregnant women in both groups (EG: 95.4%; CG: 95.1%) perceived D1, ‘breathing in a room where my partner is smoking can affect foetal development and my health’ to be a health risk. Approximately 97% of the women in both groups agreed with D2, ‘cigarette smoke from smokers in a room is harmful to me and my unborn baby’. More than half of the women in both groups (EG: 60.7%; CG: 57.0%) believed that D3 ‘toxic substances were released from things (clothes, furniture) in rooms where their partner had smoked’. Almost all women in both groups agreed with E1 ‘the harmful effects of SHS exposure on pregnant women’ (EG: 97.2%; CG: 95.1%) and E2 ‘their foetuses’ (EG: 99.1%; CG: 96.1%). Most women in both groups perceived four benefits of preventing SHS exposure: F1, ‘better growth for the foetus’ (EG: 93.5%; CG: 92.1%); F2, ‘better mental health for pregnant women’ (EG: 91.6%; CG: 96.1%); F3, ‘normal gestation for pregnant women (EG: 90.7%; CG: 88.2%)’; and F4, ‘reducing neonatal infants’ risks of heart disease and diabetes’ (EG: 89.8%; CG: 93.1%).
Less than half of the women in both groups perceived two barriers to preventing SHS exposure: G2, ‘no smoking norm or policy in the house’ (EG: 42.5%; CG: 43.5%); and G3, ‘difficulty in asking partner not to smoke inside the house’ (EG: 40.6%; CG: 34.7%). More than half of the women in both groups perceived a barrier: G4, ‘smoke-free home is a risk to routine harmonious social relations’ (EG: 56.6%; CG: 55.5%). Similarly, more than half of the women in both groups agreed with four cues to action: H1, ‘knowing what SHS is’ (EG: 66.7%; CG: 58.9%); H2, ‘knowing risks of SHS for the mother’ (EG: 73.2%; CG: 59.8%); H3, ‘knowing risks of SHS for the foetus’ (EG: 77.8%; CG: 61.8%); and H4, ‘knowing how to prevent SHS exposure in the home’ (EG: 73.2%; CG: 58.8%). In the EG, almost all women (94.5%) believed that H6, ‘brief advice from research staff on preventing SHS’ was a cue to action, while 90.5% thought H7, ‘the sticker for preventing SHS’ was a cue to action.
Secondary outcome analyses for male partners’ health beliefs and self-efficacy
An independent samples-t-test was conducted based on the assumptions of the central limit theorem [51], to assess differences in male partners’ health beliefs and self-efficacy (ST3). For most of the items, no between-group differences were observed at baseline or three months post-intervention. However, three months post-intervention, three items in cues to action showed a significant difference between groups: H1, ‘I know what SHS is’ (t-test (df = 211) = 2.40, MD = .27, 95% CI [.05, .50], p-value = .017); H2, ‘I know the risks of SHS for pregnant women’ (t-test (df = 212) = 2.55, MD = .30, 95% CI [.07, .54], p-value = .012); and H7, ‘brief advice from research staff on preventing SHS is a cue to action’ (t-test (df = 188) = 2.24, MD = .25, 95% CI [.03, .47], p-value = .025).
The cross-tabulation table (ST4) indicates male partners’ health beliefs and self-efficacy as evaluated by them at three months post-intervention. For SHS knowledge, almost all male partners (89.3–100%) in both groups selected the correct answers post-intervention. In perceived SHS-related disease susceptibility, almost all male partners in both groups (EG: 96.4%, CG: 96.1%) perceived D1, ‘breathing in a room where I am smoking cigarettes can affect foetal development and pregnant women's health risk’, as a health risk. Furthermore, 98.1% and 99.1% of the CG and EG, respectively, agreed with D2, ‘cigarette smoke from smokers in a room is harmful to pregnant women and their unborn babies’. Almost all male partners in both groups (EG: 84.4%; CG: 85.3%) agreed with D3, ‘my female partner and unborn baby breathe toxic substances which are released from things (clothes, furniture) in rooms where I smoked’. Almost all male partners in both groups perceived E1 ‘the effects of SHS on pregnant women’ (EG: 98.2%; CG: 99.1%) and E2 ‘the foetus’ (EG: 98.2%; CG: 98%).
Most male partners in both groups perceived four benefits of preventing SHS exposure: F1, ‘better growth for the foetus’ (EG: 88.2%; CG: 93.3%); F2, ‘better mental health for pregnant women’ (EG: 84.6%; CG: 92.3%); F3, ‘pregnant women’s normal gestation’ (EG: 83.6%; CG: 87.5%); and F4, ‘reducing neonatal infants’ risks of heart disease and diabetes’ (EG: 89.7%; CG: 93.2%). Less than half of male partners in both groups perceived four barriers to preventing SHS exposure: G1, ‘other smokers (visitors) do not accept the smoke-free home policy’ (EG: 45.0%; CG: 40.4%); G2, ‘no smoking norm or policy in home’ (EG: 40.4%; CG: 36.5%); G3, ‘difficulty in asking other smoker not to smoke in the house’ (EG: 40.9%; CG: 47.1%); and G5, ‘I lost social communication with other smokers (visitors) in my house’ (EG: 31.5%; CG: 38.3%). More than half of the male partners in both groups perceived G4, ‘a smoke-free home is a risk to routine harmonious social relations’ (EG: 53.6%; CG: 61.5%) as a barrier to preventing SHS exposure.