Preterm birth refers to births that occur after 28 weeks of pregnancy but before 37 weeks. Preterm infants have lower resistance compared to full-term infants and generally require special care to survive. The survival rate varies with the gestational age: at 32 to 33 weeks, the survival rate can reach 95%; at 28 to 31 weeks, it is between 90% and 95%; at 26 weeks, it is around 80%; and at 27 weeks, it is about 90%. After 34 weeks of pregnancy, the survival rate of the baby is very high, almost the same as that of a full-term baby.