How long does it take for early pregnancy reactions to appear? Detailed timeline of early pregnancy reactions are different for everyone, but there are usually similar changes, such as breast tenderness, nausea, vomiting, fatigue, etc. These reactions all reflect hormonal changes in the body. Let’s take a look at the timetable for early pregnancy reactions. Weeks 1 to 4: The fertilized egg implants in the lining of the uterus, and you may experience some minor reactions at this time, such as mild abdominal pain or light bleeding. At this time, you should try to reduce stress and excessive exercise as much as possible