**Core Concept**
The placenta produces human chorionic gonadotropin (hCG) during early pregnancy, which is a key marker for detecting pregnancy in clinical settings. hCG is secreted by the syncytiotrophoblast and has a high specificity for early gestational detection.

**Why the Correct Answer is Right**
Human chorionic gonadotropin (hCG) is the primary hormone secreted by the placenta in early pregnancy. It mimics luteinizing hormone (LH) and maintains the corpus luteum to sustain progesterone and estrogen production during the first trimester. hCG levels rise rapidly in the first 10–14 days of pregnancy and are detectable in urine and blood, forming the basis for pregnancy tests. Its presence is specific and highly sensitive in early detection.

**Why Each Wrong Option is Incorrect**
Option A: Endothelial growth factor (EGF) is involved in cell proliferation and angiogenesis but is not a primary hormone used in pregnancy detection.
Option C: Human chorionic somatotropin (HCS) is not a naturally occurring hormone and is not used in pregnancy testing.
Option D: Relaxin is a hormone that promotes joint laxity and ligament relaxation during pregnancy but is not used for early pregnancy detection.

**Clinical Pearl / High-Yield Fact**
hCG is the only hormone routinely used in urine-based pregnancy tests; its levels peak at 8–10 weeks and then decline. A positive test indicates pregnancy, and rising hCG levels are a key indicator of viable gestation.

✓ Correct Answer: B. Human chorionic gonadotropin (hCG)