A patient comes to your office with LMP 4 weeks ago. She denies any symptoms such as nausea, fatigue, urinary frequency, or breast tenderness. She thinks that she may be pregnant because she has not gotten her period yet and is very anxious to find out because she has a history of a previous ectopic pregnancy and wants to be sure to get early prenatal care. Which of the following evaluation methods is most sensitive in diagnosing pregnancy?

**Core Concept**
The diagnosis of pregnancy is a crucial step in obstetric care, particularly for patients with a history of ectopic pregnancy. The most sensitive method for diagnosing pregnancy is essential to ensure timely and appropriate management.

**Why the Correct Answer is Right**
The most sensitive method for diagnosing pregnancy is a urine human chorionic gonadotropin (hCG) test. hCG is a hormone produced by the placenta shortly after implantation of the fertilized egg into the uterus. It is detectable in the blood and urine as early as 6-8 days post-ovulation. A urine hCG test is a rapid and non-invasive method that can detect pregnancy with high sensitivity, making it an ideal initial screening tool.

**Why Each Wrong Option is Incorrect**
**Option A:** Serum hCG levels are more specific than urine hCG tests, but they are not as sensitive due to the need for venipuncture and the requirement for a laboratory to process the sample.
**Option B:** Pelvic examination is not a sensitive method for diagnosing pregnancy, as it may not detect early pregnancy or ectopic pregnancy.
**Option C:** Pregnancy tests based on luteinizing hormone (LH) levels are not as sensitive as hCG tests, as LH levels do not rise as significantly in early pregnancy.

**Clinical Pearl / High-Yield Fact**
When performing a urine hCG test, it's essential to instruct the patient to wait at least 1-2 weeks after the expected menstrual period to minimize false-negative results, as hCG levels may be too low to detect.

**Correct Answer:** B.

✓ Correct Answer: B. Serum pregnancy test