A maternity bag with a bag body defining an outer surface and a changing mat configured to be detachable from the outer surface of the body. The changing mat is optionally made of a same material as the bag body and/or has the same texture or color as the outer surface of the bag body, and is dimensioned to at least partially wrap around the outer surface of the bag body so as to be fully integrated and indistinguishable. The function and the look of the changing mat is concealed as it is integrated to the bag when attached. A method for changing babies using the bag is also provided. The changing mat being wrapped around the bag, it reinforces the body's structure and liberates space inside the bag. The invention provides an elegant and stylishly fashionable look to the bag. The invention also concerns the changing mat configured to be affixed to a diaper bag.