The invention relates to an adapter (2) for a breast shield (1) of a breast pump for pumping human breast milk. Said adapter has a chamber (280) having a first opening (282) leading to the breast shield (1) and a second opening (283) remote from the breast shield. The adapter (2) also has a flexible media separation membrane (4), which is accommodated in the chamber (280) and separates the chamber (280) into a pump-side and a breast-shield-side area. The chamber (280) tapers toward the breast-shield-side opening (282). The chamber (280) has the shape of a spherical dome which is cut off in the tapering area thereof. The media separation membrane (4) likewise has substantially the shape of a flattened spherical dome having a flat top side (411), wherein the flat top side (411) of the media separation membrane (4) faces the breast-shield-side opening (202) of the chamber (280). The adapter according to the invention permits a minimum pressure drop over the media separation membrane and ensures a reliable return to the original shape of the media separation membrane.
