Introduction:
Pregnancy presents a teachable moment to motivate smoking expectant fathers to quit smoking, but evidence from randomised controlled trials (RCT) is scarce.

Objectives:
To evaluate the effectiveness of a brief advice with nicotine replacement therapy (NRT) sampling in increase quitting in smoking expectant fathers.

Methods:
This pragmatic RCT recruits male daily cigarette smokers with a pregnant partner from antenatal clinics at seven public hospitals in Hong Kong. The participants were computer-randomised (1:1) into the intervention or control group. All participants received brief advice to quit (usual care). The intervention group additionally received offers of 1-week free sample of NRT and referral to smoking cessation services. The primary outcome is carbon monoxide-verified 7-day point-prevalence abstinence (PPA) at 6 months post-treatment initiation. Secondary outcomes at 3 months include self-reported 7-day PPA, 24-hour quit attempt, use of NRT and smoking cessation services. The target sample size is 1,148. The primary analyses were by intention-to-treat. Trial registration: ClinicalTrials.gov (NCT03671707).

Results:
Participant recruitment began in October 2018 and is expected to end by March 2020. This interim analysis included 777 participants who were randomised (384 in the intervention group and 393 in the control group) and due for 3-month follow-up on December 18, 2019 (retention rate=77.1%). Compared with the control group, the intervention group had higher rates of self-reported 7-day PPA (19.3% vs 13.2%; OR=1.57; 95% CI 1.06–2.30; P=0.023), quit attempt (41.9% vs 31.6%; OR=1.57; 95% CI 1.17–2.10; P=0.003), use of NRT (29.4% vs 1.5%; OR=26.9; 95% CI 11.7–62.0; P<0.001) and smoking cessation services (3.1% vs 1.9%; OR=2.44; 95% CI 0.93–6.42; P=0.071).

Conclusion(s):
We found preliminary evidence on the effectiveness of the brief cessation intervention. If confirmed by final analysis of all subjects, the trial would yield strong evidence to support such simple and low-cost interventions especially in Asian countries where male smoking predominates and few pregnant women smoke.