Is the questioner considered a killer for having foregone hospitalization based on the doctor's advice, which led to the death of her twin fetuses?

There is nothing upon you, because death by pressure on the umbilical cord or its entanglement is neither certain nor an action on your part. You are not obliged to seek medical treatment or hospitalization. Your refusal of the surgery is not considered a dereliction of his life or a cause of his death, and the default is the exoneration of one's liability.