The ornamental design for a maternityundergarment, as shown and described.
FIG. 1 is a perspective view of a maternity undergarment showing the new design, shown in an environment of use;
FIG. 2 is a top view of the maternity undergarment of FIG. 1;
FIG. 3 is a front view of the maternity undergarment of FIG. 1, shown in an environment of use;
FIG. 4 is a side view of the maternity undergarment of FIG. 1, shown in an environment of use;
FIG. 5 is a rear view of the maternity undergarment of FIG. 1, shown in an environment of use; and,
FIG. 6 is a bottom view of the maternity undergarment of FIG. 1.
The broken lines shown within the claimed surface of the maternity undergarment in FIG. 1 represent stitching. All other broken lines illustrate environment and form no part of the claimed design.