In Act Three of Miller's play "The Crucible," readers (or watchers) come to find out that Elizabeth Proctor is pregnant. Elizabeth has been accused (through Abigail's scheming) given that she has a poppet in her home.
When Elizabeth publicly reveals her pregnancy, she gains herself some time in facing the accusations made against her.
Puritans would not punish a woman who is pregnant. Instead, they would force her to be locked up until the time came for her to give birth. Not until after the birth of the child would Elizabeth be forced to face her charges and be named guilty or innocent of witchcraft.
Therefore, her pregnancy actually saves her life. She,possibly, would have faced a quicker trial and been put to death (with the rate the courts were finding people guilty) before the duration of a pregnancy ended.
Not only does the pregnancy save her life in this fashion, the courts find that Elizabeth is a person who always tells the truth. If she states she is pregnant, she most surely is and all else she states must be the truth. Therefore, all look to Elizabeth for the truth. The problem here lies when she is asked by the courts if her husband, John, had an affair. Elizabeth states that he had not. John was hoping that Elizabeth would tel the truth and Abigail would be called out for who she was. Unfortunately, Elizabeth lied and Abigail is still seen as needed by the courts.