[1] Univ Sussex, Sch Psychol, Brighton BN1 9QH, E Sussex, England
[2] City Univ London, Sch Hlth Sci, Ctr Maternal & Child Hlth Res, London EC1R 1UW, England
[3] Brighton & Sussex Univ Hosp Trust, Royal Alexandra Childrens Hosp, Acad Dept Paediat, Brighton BN2 5BE, E Sussex, England
[4] Bliss Special Care Baby Charity, London SE1 2EL, England
[5] Natl Childbirth Trust, London W3 6NH, England
[6] Univ Nottingham, Nottingham Clin Trials Unit, Nottingham NG7 2UH, England