**Question:** Which of the following is not helpful in the diagnosis of tubal mass in ectopic pregnancy?

A. Transvaginal ultrasound
B. Serum beta-human chorionic gonadotropin (β-hCG) level
C. Contrast-enhanced computed tomography (CT) scan
D. Serum pregnancy test

**Core Concept:**
Ectopic pregnancy is a life-threatening condition that occurs when a fertilized egg implants itself outside the uterine cavity, most commonly in the fallopian tubes. Diagnosis involves ruling out other conditions, like corpus luteal cyst and intrauterine pregnancy, and identifying the presence of a tubal mass.

**Why the Correct Answer is Right:**
Option A, transvaginal ultrasound, is the preferred diagnostic modality for assessing ectopic pregnancy due to its high sensitivity and specificity in detecting tubal masses, blood flow assessment, and visualization of the uterus and adnexa. Transvaginal ultrasound allows for better visualization of the pelvic organs and provides detailed information about the ectopic pregnancy.

**Why Each Wrong Option is Inaccurate:**
Option B, serum β-hCG level, is a crucial test for ectopic pregnancy diagnosis as it reflects the presence of a gestational sac, trophoblastic tissue, and the degree of β-hCG elevation. However, option C, contrast-enhanced computed tomography (CT) scan, is less specific and more radiation-exposing compared to ultrasound. Although CT can be helpful in certain situations, it is not as sensitive or specific as ultrasound in detecting tubal masses.

Option D, serum pregnancy test, is less reliable than β-hCG level measurement as it only confirms the presence of a pregnancy but cannot differentiate between intrauterine and ectopic pregnancies.

**Clinical Pearl:**
Relying solely on a positive serum pregnancy test should not be the sole basis for suspecting or diagnosing ectopic pregnancy. A combination of clinical evaluation, β-hCG level analysis, and imaging studies (ultrasound) are essential for accurate diagnosis and appropriate management of ectopic pregnancy.