Is expiation or fasting incumbent upon one whose fetus died in the seventh month after she left the hospital against doctors' advice to care for her daughter?

It does not appear that you bear any responsibility for refusing hospitalization, because high blood pressure can lead to fetal death even if hospitalization and treatment are administered. Moreover, seeking medical treatment is not obligatory according to the majority of Imams. Your refusal of hospitalization is not considered negligence concerning the fetus's life or a cause of its death.