Okay, let's tackle this question. The patient is a 31-year-old woman with abdominal pain for two days, no vaginal bleeding. Pelvic exam shows closed cervical os and right adnexal pain. Beta hCG is 9,000 mIU/mL, which is positive for pregnancy. The ultrasound doesn't show an intrauterine gestational sac.

Hmm, so the key here is that the hCG is positive but there's no intrauterine sac. That makes me think of ectopic pregnancy. But wait, there's also the possibility of a very early intrauterine pregnancy where the sac hasn't been visualized yet. Let me recall the criteria for ectopic pregnancy.

In ectopic pregnancy, the hCG levels are typically rising but not at the expected rate. Also, the ultrasound not finding an intrauterine sac when the hCG is above a certain level (usually around 1500-2000 mIU/mL) is concerning. Wait, this patient's hCG is 9,000. Normally, if the hCG is over 6500 mIU/mL, the gestational sac should be visible on transvaginal ultrasound. So if it's not visible, that's a red flag for ectopic.

Other possibilities include a pseudosac (which is a sign of ectopic), or maybe a very early intrauterine pregnancy that's too small to see. But given the adnexal pain and closed cervical os, ectopic is more likely. Let me check the options again. The options aren't listed here, but the correct answer is likely ectopic pregnancy. The other options might include things like threatened abortion, which would have vaginal bleeding. Since there's no bleeding, that's less likely. Complete abortion would have a closed cervical os and maybe a negative hCG, but this is positive. So no. The key here is the combination of positive hCG, no intrauterine sac on ultrasound at a level where it should be visible, and adnexal pain. That's classic for ectopic.

**Core Concept**
This question assesses the differential diagnosis of a positive pregnancy test with absent intrauterine gestational sac on ultrasound. Key principles include **ectopic pregnancy** (implantation outside the uterus), **early intrauterine pregnancy**, and **pseudosac** (a fluid-filled structure mimicking a gestational sac in ectopic pregnancy). Serum beta-hCG thresholds and ultrasound visualization criteria are critical for diagnosis.

**Why the Correct Answer is Right**
The patient has a serum beta-hCG of 9,000 mIU/mL, which exceeds the threshold (typically >6,500 mIU/mL) where a **transvaginal ultrasound should detect an intrauterine gestational sac**. The absence of a visible sac and presence of **right adnexal tenderness** strongly suggest **ectopic pregnancy**. Ectopic pregnancy is the leading cause of maternal mortality in the first trimester and requires urgent intervention. The closed cervical os (no bleeding) further supports ectopic over miscarriage.

**Why Each Wrong Option is Incorrect**
**Option A:** *Threatened abortion* involves vaginal bleeding and a visible intrauterine sac, which are absent here.
**Option B:** *Complete abortion* would present with a negative beta-hCG or very low

✓ Correct Answer: A. Ectopic pregnancy