How long does severe hypoxia associated with premature baby last?

It varies: Near the end of the 2nd trimester, certain areas of the fetal brain are particularly susceptible to drops in oxygen/ low blood flow, which can be caused by maternal conditions that necessitate early delivery for the safety of the mother or because fetal well-being is found to be compromised. Ob's get those babies out asap & neonatologists try to prevent further hypoxia, but the die may be cast.