**Question:** Earliest pregnancy is detected by

A. Ultrasound
B. Serum Human Chorionic Gonadotropin (hCG) levels
C. Lactulose breath test
D. Digital rectal examination

**Correct Answer:** A. Ultrasound

**Core Concept:** Human pregnancy is a physiological condition characterized by the growth and development of an embryo within the uterus. Ultrasound, a non-invasive medical imaging technique, utilizes high-frequency sound waves to create images of internal structures and organs, including the fetus in pregnancy.

**Why the Correct Answer is Right:** Ultrasound is the right answer because it enables early detection of pregnancy by visualizing the presence of a gestational sac, fetal poles, and fetal heartbeat, indicating fetal development and viability. This typically occurs around the 6th to 7th week of pregnancy.

**Why Each Wrong Option is Incorrect:**

A. **Ultrasound (Option A)** is the correct method for early pregnancy detection due to its ability to visualize fetal structures.

B. **Serum Human Chorionic Gonadotropin (hCG) levels (Option B)** are used to confirm ongoing pregnancy, not detect early pregnancy. hCG is a hormone produced during pregnancy that rises rapidly after fertilization, peaking in the first trimester and then decreasing.

C. **Lactulose breath test (Option C)** is a diagnostic procedure used in the diagnosis of liver disorders, particularly liver cirrhosis, and is not relevant to detecting early pregnancy.

D. **Digital rectal examination (Option D)** is a physical examination method primarily used in assessing prostate health and is not suitable for detecting early pregnancy.

**Clinical Pearl:** Early pregnancy detection is crucial for patient counseling, obstetric management, and appropriate medical intervention. Ultrasound remains the gold standard for confirming pregnancy and assessing fetal viability.