Abstract: The present invention relates to a system, method and corresponding computer program for milk ejection reflex (MER) determination, the system comprising a breast shield arrangement (1) for a breast pump (2) configured to be attached on a first breast of a female, a physiological sensor unit (4) for receiving a physiological reception signal from the second breast, which is opposite to the first breast, wherein the physiological reception signal is indicative of fluid contents in the second breast, and wherein the system is configured to determine a milk ejection reflex based on a change in fluid contents in the second breast. It finds particular application during and in connection with breastfeeding and allows for direct detection of the beginning of the milk flow in the breast, i.e. the occurrence of the MER, without delay and with a high degree of precision.