An 'elective' amneocentisis can be rejected by either parent in the US. However, most applications of these tests are not elective, but rather forced by a doctor to either protect the life of the baby or the mother. Performing this test to determine the genetic make-up of the unborn child is not the primary function of the test. Securing the safety of the mother & child (whether genetically diseased or not) is paramount.

Thus, assuming your 1 in 50 shot of the child dying, I would postulate that the test isn't forced on the mother unless there is a greater than 1 in 50 shot either the mother or child dies without the added information of the test.

Edited: The comments in the first paragraph were learned from my wife's doctor not 1 month ago.