Having characteristics opposite those associated with maternity
2007, Jill Rudd, Val Gough, Charlotte Perkins Gilman: Optimist Reformer[1], →ISBN, page 207:
The eponymous "Unnatural Mother," for one, certainly seems to show an antimaternal rather than a maternal reflex when she rapidly and automatically acts to save her town rather than her own child.
(immunology) Pertaining to an immune response against the mother