When does serum HCG rapidly rise during gestation?

The serum human chorionic gonadotropin (HCG) levels are known to rise rapidly during the early stages of pregnancy, typically peaking around the time of implantation and shortly thereafter. The most significant rise in serum HCG levels is generally observed around the end of the first trimester, which is approximately 30 to 40 days after the last menstrual period. Specifically, around 41 days into gestation, HCG levels have reached significant peaks and are often more than doubled every 48 to 72 hours during the early weeks. This is crucial for confirming a healthy pregnancy, as it indicates that the placenta is developing and that the body is recognizing and supporting the growth of the embryo.

In other options provided, 14 days (or around two weeks) marks a time when HCG could be detected but is not at its peak, 21 days is still early in the gestation timeframe, and while there may be some increase, it does not reflect the rapid rise observed as the pregnancy progresses. Therefore, the peak at around 41 days is the most accurate choice since it aligns with the typical gestational timeline for HCG elevation.