A breast shield unit of a breast pump for expressing human breastmilk comprises a breast shield to be placed onto a mother's breast, a breastmilk collection container for receiving expressed breastmilk, an adapter for connecting the breast shield to the breastmilk collection container and a valve head. A breastmilk channel extends from the breast shield into the breastmilk collection container through the adapter and the valve head. The valve head includes a valve which closes and opens the breastmilk channel during the pumping action, wherein a fill level sensor for measuring a fill level of the breastmilk collection container is arranged in the valve head. The breast shield unit according to the invention facilitates a fill level measurement without a structural change of the breast shield and breastmilk collection container. Moreover, it facilitates data interchange with external information storage and/or information processing units.