A 28-year-old woman presents with 6 weeks amenorrhea, lower abdominal pain, and vaginal spotting. On examination, she has cervical motion tenderness and a palpable adnexal mass. Urine β-hCG is positive. What is the investigation of choice to confirm the diagnosis of ectopic pregnancy?

Explanation

## Investigation of Choice for Ectopic Pregnancy Confirmation ### Transvaginal Ultrasound: Gold Standard **Key Point:** Transvaginal ultrasound is the investigation of choice for diagnosis and localization of ectopic pregnancy. It has 90–95% sensitivity and 98% specificity when performed by experienced operators. ### Why Transvaginal Ultrasound? 1. **Superior resolution:** Transvaginal probe provides better visualization of the adnexa compared to transabdominal approach, especially in early pregnancy (5–7 weeks gestation). 2. **Non-invasive:** No radiation exposure; safe in pregnancy. 3. **Real-time assessment:** Allows direct visualization of: - Empty uterine cavity (rules out intrauterine pregnancy) - Gestational sac in fallopian tube, ovary, or peritoneal cavity - Fetal cardiac activity (if present) - Free fluid in pelvis (suggests rupture) 4. **Cost-effective:** Readily available in most centers; no need for advanced imaging. ### Ultrasound Findings in Ectopic Pregnancy | Finding | Significance | | --- | --- | | Empty uterine cavity + positive hCG | Ectopic until proven otherwise | | Adnexal gestational sac with yolk sac | Confirms ectopic pregnancy | | Adnexal mass with free fluid | Suggests rupture; emergency | | Pseudosac (central location) | Intrauterine pregnancy; may coexist with ectopic | **Clinical Pearl:** A **pseudosac** (fluid collection within the endometrial cavity) can mimic early intrauterine pregnancy and lead to diagnostic error. The presence of a yolk sac or fetal pole confirms intrauterine pregnancy. **High-Yield:** In the absence of an intrauterine gestational sac with a positive hCG >1500 mIU/mL, ectopic pregnancy must be suspected and transvaginal ultrasound performed urgently. ### Role of Serum β-hCG While serum β-hCG quantification is important for **risk stratification** and **prognostic assessment**, it is **not diagnostic** of ectopic pregnancy. Serial hCG measurements (48-hour interval) help differentiate: - Normal intrauterine pregnancy: hCG doubles every 48–72 hours - Ectopic/failing pregnancy: slower rise or plateau **Warning:** Serum hCG alone cannot localize the pregnancy and should never delay ultrasound in a symptomatic patient. ### Why Other Options Are Suboptimal **Diagnostic laparoscopy:** Invasive procedure reserved for hemodynamically unstable patients with suspected rupture or when ultrasound is inconclusive and clinical suspicion is high. Not first-line for diagnosis. **CT abdomen and pelvis:** Exposes the patient to radiation; lower sensitivity than ultrasound for early ectopic pregnancy. Reserved for ruling out other diagnoses (appendicitis, ovarian torsion) when ultrasound is equivocal. [cite:DC Dutta's Textbook of Obstetrics Ch 7]