## **Core Concept**
The human chorionic gonadotropin (hCG) is a hormone produced during pregnancy that is made by the developing embryo after conception and later by the placental component syncytiotrophoblast. It plays a critical role in maintaining the corpus luteum during the beginning of pregnancy. The levels of hCG can be detected in blood and urine, and they are crucial for confirming pregnancy.

## **Why the Correct Answer is Right**
The plasma levels of hCG during a normal pregnancy approximately double every 48 hours during the first trimester. This rapid increase is significant in early pregnancy for confirming a viable intrauterine pregnancy. The mechanism behind this doubling time is related to the rapid growth and development of the trophoblastic cells of the embryo, which produce hCG. This characteristic doubling time is a guideline used in assessing the health and progression of early pregnancy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 24 hours - While hCG levels do rise rapidly, they do not double as frequently as every 24 hours; this option underestimates the doubling time.
- **Option C:** 72 hours - This option overestimates the doubling time; hCG levels typically increase more rapidly than this.
- **Option D:** 96 hours - This option significantly overestimates the doubling time of hCG levels during early pregnancy.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that while hCG levels typically double every 48 hours, there can be variations. A slower increase might suggest a potential issue with the pregnancy, but it's also important to consider other factors such as the initial level of hCG and the overall clinical context.

## **Correct Answer:** B. 48 hours.