In the early pregnancy, the doubling time of HCG concentrations in plasma is :
**Core Concept**
Human chorionic gonadotropin (HCG) is a hormone produced by the placenta during pregnancy. Its concentration in plasma is a critical marker for early pregnancy detection and assessment. The doubling time of HCG concentrations is an essential parameter in evaluating the viability and progression of early pregnancy.
**Why the Correct Answer is Right**
The doubling time of HCG concentrations in early pregnancy typically ranges from 48 to 72 hours. This rapid increase is due to the high sensitivity of the HCG-producing syncytiotrophoblast cells to the trophoblastic hormone, which stimulates the production of HCG. The initial surge in HCG levels is a result of the implantation of the blastocyst into the uterine lining and the subsequent development of the placenta. As the placenta matures, the production of HCG gradually decreases, and its concentration in plasma stabilizes.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the doubling time of HCG concentrations is typically longer than 24 hours in early pregnancy.
* **Option B:** This option is incorrect because the doubling time of HCG concentrations is not fixed and can vary depending on individual factors, such as the presence of multiple gestations or placental dysfunction.
* **Option D:** This option is incorrect because the doubling time of HCG concentrations is not typically longer than 96 hours in early pregnancy.
**Clinical Pearl / High-Yield Fact**
A rapid increase in HCG concentrations with a doubling time of 48-72 hours is a strong indicator of a viable intrauterine pregnancy. Conversely, a plateau or decrease in HCG levels may suggest a failed pregnancy or ectopic pregnancy.
**Correct Answer:** C. 48-72 hours