Understanding the hormones behind the timeline helps explain why symptoms appear when they do. After ovulation, progesterone rises regardless of pregnancy — this is what causes PMS symptoms. If implantation occurs, the embryo begins producing hCG, which signals the corpus luteum to keep making progesterone.
hCG doubles every 48 to 72 hours in early pregnancy (see our hCG levels guide for week-by-week ranges). Rising hCG is responsible for nausea, breast changes, and fatigue. Estrogen also climbs rapidly, contributing to heightened smell sensitivity and food aversions.
By week 5, most people are noticing clear symptoms. By week 6, morning sickness often kicks in and fatigue becomes harder to ignore. These symptoms typically peak around weeks 8 to 11 and begin improving in the second trimester.