The correct spelling of the word indicating the most severe level of fetal distress is "most foetal" in British English and "most fetal" in American English. The pronunciation of both spellings is the same: /məʊst fiːtəl/ or /məʊst fiːt(ə)l/. The word "fetal" refers to the period of development inside the uterus, while "distress" implies harm or danger. It is crucial for medical professionals and expectant parents to understand and recognize the signs of fetal distress to ensure the health and safety of the baby.