**Question:** True about hCG is:

A. It is a hormone produced by the placenta during pregnancy to maintain the corpus luteum and stimulate the ovaries to produce estrogen and progesterone.
B. hCG is identical to the human chorionic gonadotropin hormone involved in regulating the menstrual cycle.
C. hCG levels remain constant throughout pregnancy and do not increase with advancing gestation.
D. hCG levels peak in the second trimester of pregnancy and then decrease gradually.

**Correct Answer:**

**Core Concept:** Human chorionic gonadotropin (hCG) is a glycoprotein hormone that plays a crucial role in pregnancy. It is produced by the syncytiotrophoblast cells in the placenta and acts as a trophoblast-derived hormone.

**Why the Correct Answer is Right:**

hCG is indeed a key hormone during pregnancy, responsible for maintaining the corpus luteum and stimulating the ovaries to produce estrogen and progesterone. Its primary function is to ensure a sustained pregnancy by promoting the growth and differentiation of the placenta.

**Why Each Wrong Option is Incorrect:**

A. This statement is partially correct but lacks the information about the constant production of hCG throughout pregnancy. The hormone does play a role in maintaining the corpus luteum and stimulating the ovaries, but it continues to increase with advancing gestation.
B. This option focuses on the menstrual cycle, which is not the main purpose of hCG. hCG is primarily involved in pregnancy and does not regulate the menstrual cycle.
C. The correct answer states that hCG levels remain constant throughout pregnancy. In reality, hCG levels increase with advancing gestation, reflecting the growth and development of the placenta.
D. This statement is consistent with the correct answer, as hCG levels peak in the second trimester of pregnancy and then decrease gradually. This pattern reflects the physiological changes during pregnancy, such as the increased demand from the growing fetus.

**Clinical Pearl:**

Understanding the dynamics of hCG levels during pregnancy is essential for physicians and healthcare professionals. Monitoring hCG levels can provide valuable information about gestational age, potential complications, and fetal viability. A rising hCG trend indicates a healthy pregnancy, while a decreasing or plateauing trend may be a sign of threatened miscarriage or ectopic pregnancy.