Smoking, nicotine and pregnancy 2 (SNAP2) trial: protocol for a randomised controlled trial of an intervention to improve adherence to nicotine replacement therapy during pregnancy by Clark, MM, Cooper, S, Naughton, F, Ussher, M, Emery, J, McDaid, L, Thomson, R, Phillips, L, Bauld, L, Aveyard, P, Torgerson, D, Berlin, I, Lewis, S, Parrott, S, Hewitt, C, Welch, C, Parkinson, G, Dickinson, A, Sutton, S, Brimicombe, J, Bowker, K, McEwen, A, Vedhara, K, Coleman, T