What body system defends the body against pathogens after they enter the bloodstream?

Emma recently found out she was pregnant. every thursday evening for the next six weeks, emma and her mother will attend a special program that prepares pregnant teens to become mothers. during the first class, emma learned about the stages of childbirth. what was the order she was taught? first, emma learned about  .then, she learned about the    stage. next, emma learned about  .last, she learned about the    stage