Contrary to the coils used today, the Dalkon Shield was unsafe and dangerous. The coil was rather large and accordingly difficult to insert and remove.
As a result, the retrieval threads consisted of several threads plaited together (multifilament) which worked as a “ladder” for bacteria. The retrieval threads of other coils consist of just one single thread (monofilament).
Read also the paper by Kathryn Goldberg Designing the popularity of the dalkon shield