The aim of this randomized controlled trial was to determine whether a behavioural intervention in pregnancy supported by online information would improve smoking cessation rates. However, due to a number of challenges, recruitment to this trial was reluctantly halted. We aimed to recruit 220 maternal smokers within 2 years and after screening 1995 women, just 22 enrolled over a 8-month period. Only three women accessed the online element of the intervention and, at follow up, no women reported quitting. We report our findings as they may inform the design and powering of future smoking cessation interventions in pregnancy.