What is the ruling of the Sharia on my refusal to have a C-section to preserve the life of the fetus, whom doctors have diagnosed with delayed growth, and my wish for its death?

If the question from the inquirer is about the ruling on her supplicating for the death of her fetus, then this is a forbidden transgression in supplication. She could have instead asked for well-being and safety for both herself and the fetus.

If her question is about the ruling on her refusal of the doctors' request to perform a Cesarean section, and the danger to the fetus was certain, then she erred in her refusal. It was obligatory for her to comply with the doctors' request to save the life of the fetus from perishing, as surgical delivery is considered necessary when doctors fear for the life of the mother, the fetus, or both.