In a woman with early pregnancy, β‑hCG rising from 300 to 1,000 mIU/mL in 48 hours and trans‑vaginal ultrasound now showing an empty ring‑like structure in the right adnexa with no intra‑uterine sac, what is the most likely diagnosis and what should be the immediate next step in management?

Ectopic Pregnancy with Rising β-hCG and Adnexal Ring Structure

In this woman with β-hCG rising from 300 to 1,000 mIU/mL over 48 hours and a ring-like structure now visible in the adnexa on ultrasound, the most likely diagnosis is ectopic pregnancy, and the immediate next step is to obtain immediate gynecology consultation for medical management with methotrexate or surgical intervention. 1

Diagnostic Interpretation

β-hCG Pattern Analysis

• The β-hCG rise from 300 to 1,000 mIU/mL represents a 233% increase over 48 hours, which exceeds the 53% minimum rise expected in viable intrauterine pregnancy 2
• However, the presence of an adnexal ring structure with no intrauterine gestational sac at β-hCG 1,000 mIU/mL is highly suspicious for ectopic pregnancy 3, 4
• Approximately 22% of ectopic pregnancies occur at β-hCG levels below 1,000 mIU/mL, demonstrating that ectopic pregnancy can present at any β-hCG level 2

Ultrasound Findings Evolution

• The progression from "hazy adnexa" to "less hazier adnexa" to now a "ring-like structure in adnexa" represents evolving visualization of an ectopic gestational sac 5, 4
• An extraovarian adnexal mass (ring-like structure) without intrauterine pregnancy has a positive likelihood ratio of 111 for ectopic pregnancy 2, 1
• The absence of an intrauterine gestational sac at β-hCG 1,000 mIU/mL is concerning, as a gestational sac typically becomes visible on transvaginal ultrasound at approximately 1,000-2,000 mIU/mL 2

Immediate Management Algorithm

Step 1: Confirm Diagnosis with Transvaginal Ultrasound

• Perform transvaginal ultrasound immediately (if not already done) to definitively characterize the adnexal ring structure, as transvaginal ultrasound has 99% sensitivity for detecting ectopic pregnancy when β-hCG levels are elevated 3, 4
• Document the following findings: 2
  • Presence/absence of intrauterine gestational sac in the upper two-thirds of the uterus
  • Characteristics of the adnexal mass (size, presence of yolk sac or embryo, cardiac activity)
  • Free fluid in the pelvis or cul-de-sac (suggests possible rupture)
  • Bilateral adnexal evaluation

Step 2: Assess Hemodynamic Stability

• Evaluate for peritoneal signs, severe unilateral pain, shoulder pain (suggesting hemoperitoneum), or hemodynamic instability 2, 1
• If the patient has peritoneal signs or hemodynamic instability, immediate surgical intervention is required 5

Step 3: Obtain Immediate Gynecology Consultation

• Given the β-hCG level of 1,000 mIU/mL with an adnexal ring structure and no intrauterine pregnancy, immediate specialty consultation is mandatory 3, 1
• This represents a high-risk pregnancy of unknown location with approximately 57% probability of ectopic pregnancy when β-hCG is above 1,000 mIU/mL without intrauterine visualization 2

Treatment Decision Framework

Medical Management Criteria (Methotrexate)

Methotrexate is appropriate if ALL of the following criteria are met: 1

• Hemodynamically stable patient
• β-hCG ≤10,000 mIU/mL (current level 1,000 mIU/mL meets this criterion)
• Adnexal mass ≤5 cm
• No fetal cardiac activity detected
• No signs of rupture
• Patient able to comply with close follow-up

Methotrexate protocol: 1

• Single-dose regimen: 50 mg/m² intramuscularly
• β-hCG monitoring on days 4 and 7, then weekly until levels reach zero
• Expected pattern: initial rise on day 4, then decline by day 7
• Second dose may be needed in approximately 12% of patients if β-hCG fails to decline appropriately
• Success rate: 91-94% when inclusion criteria are properly followed

Surgical Management Indications

Immediate surgery is required if ANY of the following are present: 5

• Peritoneal signs or hemodynamic instability
• Initial β-hCG level very high (>10,000 mIU/mL)
• Fetal cardiac activity detected outside the uterus
• Contraindication to methotrexate
• Patient unable to comply with close follow-up
• Adnexal mass >5 cm

Critical Pitfalls to Avoid

• Never use β-hCG value alone to exclude ectopic pregnancy when ultrasound findings are indeterminate—this is a Level B recommendation 2, 3
• Do not defer transvaginal ultrasound based on "low" β-hCG levels, as ectopic pregnancies can rupture at any β-hCG level 2
• Avoid premature diagnosis of nonviable intrauterine pregnancy based solely on absence of intrauterine gestational sac at this β-hCG level without positive ectopic findings 3
• Do not initiate treatment based solely on absence of intrauterine pregnancy without positive findings of ectopic pregnancy 2
• The traditional discriminatory threshold of 3,000 mIU/mL has virtually no diagnostic utility (positive likelihood ratio 0.8, negative likelihood ratio 1.1) and should not delay diagnosis or treatment 2, 3

Patient Safety Instructions

Instruct the patient to return immediately for emergency evaluation if: 1

• Worsening or severe abdominal pain, especially unilateral
• Shoulder pain (suggests hemoperitoneum)
• Heavy vaginal bleeding (soaking a pad per hour)
• Dizziness, syncope, or lightheadedness
• Any signs of hemodynamic instability

Follow-up Protocol

• If methotrexate is administered, serial β-hCG measurements are essential on days 4 and 7, then weekly until levels reach zero 1
• Approximately 3-6% of patients treated with methotrexate will require surgery for rupture despite appropriate selection 1
• Continue monitoring until β-hCG reaches <5 mIU/mL to confirm complete resolution 2