Spalding 'sign' occurs because of:

Spalding sign occur due to intrauterine maceration. Spalding sign is a radiological sign which indicates the overlapping of skull bones. Overlapping of skull bones occur due to shrinkage of cerebrum and due to violent contractions of the uterus in an attempt to expel the dead fetus. Characteristic features of intrauterine maceration are: Dead body will be soft, flaccid, edematous, and flattened, when placed on flat surface it will remain straight and flat without showing the normal curvatures. Coppery red or flesh like or brownish red in colour. Emits a sweet but disagreeable smell. Serous cavities will contain turbid reddish fluid. Body surface presents with large blebs resembling pemphigus containing red serous or serosanguinous fluid. Evidence of Spalding's sign. Ref: Forensic Medicine and Toxicology By R.N. Karmakar page 25.