Background: Cigarette smoking is a leading preventable factor associated with complications in pregnancy including preterm birth and low birthweight. Past interventions have raised cessation rates by approximately 6% overall (Lumley et al. 2009). Methods: A three-part literature review, two qualitative studies with a total of 36 participants, and the development of an intervention to promote smoking cessation during pregnancy were completed. Central to the design of the research was the creation of the theoretical basis which was developed in line with recommendations from the MRC Framework for Complex Interventions (Craig et al. 2008, Campbell et al. 2000). For part one of the literature review, 24 qualitative and 44 quantitative studies were re-analysed to complete a mixed-methods secondary analysis of the active ingredients in interventions to promote smoking cessation during pregnancy. Part two consisted of an exploration of psychological models and constructs which are likely to predict or influence smoking behaviour during pregnancy. The final part was a discussion regarding the modes of delivery by which an intervention could feasibly be delivered. Qualitative interviews were carried out with participants from stakeholder groups to fill in gaps in literature and determine the acceptability and feasibility of the proposed intervention. The intervention was created using the theoretical basis developed from the findings. Further qualitative interviews, a focus group, and heuristic evaluation were used to determine the acceptability and usability of the intervention for the target group of pregnant smokers. Results and Conclusions: Findings from this work are potentially relevant for a wide range of behaviours and behavioural interventions. An intervention which has a strong grounding in theory and evidence, and is acceptable and feasible for the target group and in clinical practice was developed using evidence gathered in this thesis.

[Truncated abstract] With the dramatic rise in asthma and allergic disease there is an urgent need to define the early life exposures which influence developing immune responses to increase the predisposition to allergic disease. While this is clearly multifactorial, this thesis addresses the effects of maternal smoking as a major adverse, yet avoidable exposure in early life. I hypothesised that the well-documented increased susceptibility to infection in infants of smokers could indicate underlying effects on innate Toll-like receptor (TLR) mediated microbial responses which could in turn contribute to early immune dysregulation and increased risk of allergic disease. In addition to providing the first defence against microbes, TLR-mediated pathways modulate subsequent specific immune response and are of growing interest in the potential inhibition of inappropriate allergic responses. My initial interest in the potential immune effects of smoking in pregnancy was based on preliminary retrospective analyses of a previous cohort (presented in Chapter 3) which suggested possible effects on T cell cytokine responses to mitogens and allergens. Based on this, I recruited a new prospective pregnancy cohort (n=122) of smokers (n=60) and non-smokers (n=62) (as outlined in Chapter 4) to confirm this and test my novel hypothesis that maternal smoking may be affecting important innate (TLR-mediated) immune pathways. … Thus, these findings could indicate that smoking increases the early susceptibility to infection thereby increasing subsequent IgA responses. This is supported by observations that key neonatal TLR responses are attenuated in children who go onto develop wheezy illnesses and lower respiratory tract infections. Together, the study findings suggest that in addition to effects on lung growth, maternal smoking may also influence aspects of neonatal innate immune function that are now believed to play a critical role in microbial-driven postnatal immune development, highlighting that other environmental interactions are also highly relevant to the v