Being underweight at pregnancy commencement is associated with a range of adverse maternal and infant outcomes, as is being overweight or obese, yet it is an aspect of maternal health which has been relatively neglected by healthcare professionals and researchers. We aimed to investigate differences in pre-pregnancy and pregnancy healthy lifestyle advice routinely offered by relevant healthcare professionals, including midwives and GPs, to women across three different BMI categories - underweight, normal, and overweight or obese.