**Core Concept:**
A woman presenting with postmenopausal bleeding, abdominal pain, and a positive urine human chorionic gonadotropin (hCG) test, but an ultrasound scan not showing an adnexal mass or intrauterine pregnancy. This case represents a clinical scenario of ectopic pregnancy.

**Why the Correct Answer is Right:**
The correct answer is D ("Investigation of choice is serum beta hCG"). In this case, because the urine hCG test is positive, it indicates a pregnancy-related issue. The next logical step would be to confirm the pregnancy status and monitor its progression. Serum beta hCG levels are more accurate than urine hCG tests since they can detect lower levels of the hormone.

**Why Each Wrong Option is Incorrect:**
A. Transvaginal ultrasound (TVUS) is not the most appropriate initial test, despite being non-invasive, because the patient has a positive urine hCG test which already indicates a pregnancy-related issue.
B. The patient's general condition is satisfactory, and the abdominal pain and bleeding are more concerning for an ectopic pregnancy. However, no definitive diagnosis is made with this information alone.
C. The ultrasound scan does not reveal an adnexal mass or intrauterine pregnancy, which is a necessary but insufficient condition to diagnose an ectopic pregnancy.

**Clinical Pearl:**
Ectopic pregnancy is a life-threatening condition that requires urgent management. The next step in the diagnostic process is to confirm the pregnancy status and monitor beta hCG levels over time. If the beta hCG level continues to rise or if the patient's symptoms worsen, further diagnostic tests, such as a beta hCG ratio test or transvaginal ultrasound, may be performed.