Final answer:
Morning sickness usually occurs during the first trimester of pregnancy and is characterized by nausea and vomiting.
Step-by-step explanation:
Morning sickness usually occurs during the first trimester of pregnancy, which lasts for about 12 weeks. It is characterized by nausea and vomiting, but it can happen at any time of the day, not just in the morning. The cause of morning sickness is believed to be the increased circulation of pregnancy-related hormones, such as estrogen, progesterone, and hCG, as well as decreased intestinal peristalsis.