A method of providing an indication as to the amount of milk remaining in a breast during lactation based on a determined fat content of milk that has been expressed from said breast is disclosed. The method of determining said fat content comprises measuring an optical characteristic of milk following expression and by comparing said measured optical characteristic with data representing a corresponding optical characteristic of a sample of milk having a known fat content to determine the fat content of said expressed milk which is indicative of the amount of milk remaining in the breast.