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OG9.4 | Ectopic Pregnancy and Acute Abdomen — SDL Guide

Learning Objectives

• Define ectopic pregnancy and describe its common sites with approximate frequency
• Describe the clinical presentation of ectopic pregnancy including the differential diagnosis of acute abdomen in early pregnancy
• Explain the pathophysiology of tubal ectopic pregnancy and the risk factors that predispose to it
• Select and interpret investigations for suspected ectopic pregnancy using the serum β-hCG/TVS algorithm
• Enumerate the strict criteria for medical management with methotrexate and contrast salpingostomy versus salpingectomy
• Outline the emergency management of a haemodynamically unstable patient with ruptured ectopic pregnancy

INSTRUCTIONS

Ectopic pregnancy is a life-threatening surgical emergency that simultaneously tests your diagnostic reasoning, your knowledge of anatomy, and your ability to act quickly under uncertainty. It is the commonest cause of maternal death in the first trimester, responsible for approximately 3–4% of all pregnancy-related deaths in India. This module takes you through the full clinical arc: from the woman presenting with vague lower abdominal pain and a positive pregnancy test, through the β-hCG/ultrasound algorithm, to the management decision between expectant waiting, methotrexate, and laparoscopic surgery. Every section builds on the last — read them in order. The known-traps section on methotrexate criteria and salpingostomy vs salpingectomy indications are high-yield viva topics.

References

• DC Dutta's Textbook of Obstetrics, 9th ed, Chapter 11 (textbook)
• Williams Obstetrics, 26th ed, Chapter 19 (textbook)
• RCOG Green-top Guideline No. 21 — Diagnosis and Management of Ectopic Pregnancy, 2016 (guideline)
• ASRM Practice Committee Opinion — Medical Treatment of Ectopic Pregnancy, 2013 (guideline)

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Version 2.0 | NMC CBUC 2024

Clinical Presentation of Ectopic Pregnancy

Ectopic pregnancy is the implantation and development of the fertilised ovum at a site other than the uterine cavity. The vast majority (95–98%) occur in the fallopian tube. Every medical student memorises the classic clinical presentation, but the dangerous clinical reality is that many ectopic pregnancies do not present with the textbook triad — up to 50% of women who die from ruptured ectopic have been seen by a clinician in the preceding 24–48 hours, who missed the diagnosis because the presentation was atypical. The woman may report only mild, intermittent pain and attribute her missed period to stress. She may have no obvious vaginal bleeding. She may have seen a doctor, been reassured, and returned in extremis with haemorrhagic shock. The clinician who restricts the differential to 'threatened abortion' or 'gastritis' in any woman of reproductive age with lower abdominal pain will, statistically, miss an ectopic. Maintaining a high index of suspicion — and using the β-hCG/TVS algorithm systematically — is the only reliable protection against this diagnostic error.

The classic triad of ectopic pregnancy is:
1. Amenorrhoea — typically 6–8 weeks of absent menses (shorter if isthmic, longer if ampullary)
2. Lower abdominal/pelvic pain — often unilateral; may be vague or sudden and severe (if rupture occurs); shoulder-tip pain (diaphragmatic irritation by haemoperitoneum) is a red-flag symptom
3. Vaginal bleeding — usually scanty, dark ('old blood'); distinguishable from the heavier red bleeding of incomplete abortion (but not always reliable)

On examination:
- Vital signs: may be haemodynamically stable (unruptured) or unstable (ruptured — HR >100, SBP <90, pallor, syncope)
- Abdominal: lower abdominal tenderness; guarding and rebound if peritoneum is irritated by haemoperitoneum; shoulder-tip tenderness if significant intraperitoneal bleeding
- Pelvic examination: cervical os CLOSED (distinguishes from inevitable/incomplete abortion); cervical excitation tenderness (pain on moving the cervix — adnexal pathology = pain when tube is palpated via cervical movement); adnexal mass may be palpable

Differential diagnosis of acute abdomen in early pregnancy — this is the core clinical reasoning challenge:

• Ectopic pregnancy: closed os, adnexal mass/tenderness, cervical excitation, haemoperitoneum signs if ruptured; positive hCG
• Threatened/inevitable abortion: bleeding, uterus size = dates, open os (inevitable), USG may show live fetus or failing IUP
• Incomplete abortion: open os, tissue passed or retained, uterus smaller than dates
• Ruptured corpus luteum cyst: no intrauterine pregnancy expected; may present identically to ectopic; negative or very low hCG distinguishes
• Ovarian cyst accident (torsion or rupture): adnexal mass on USG, may be afebrile; Doppler shows absent or reduced flow in torsion
• Appendicitis: right iliac fossa tenderness at McBurney's point, Rovsing's sign, fever, raised WBC; positive pregnancy test does not exclude — appendicitis is the most dangerous non-obstetric diagnosis to miss in a pregnant woman
• Pelvic inflammatory disease (PID): bilateral adnexal tenderness, cervical discharge, fever; closed os; lower hCG level
• Degeneration in fibroid: if previous fibroids known; USG shows fibroid with heterogeneous core

Provided image

Pathophysiology and Sites of Ectopic Implantation

The fertilised ovum normally completes its journey from the ampulla of the fallopian tube to the uterine cavity in approximately 3 days, propelled by coordinated tubal peristalsis and the rhythmic sweeping of the mucosal cilia lining the tube. This finely timed transport is necessary for the embryo to reach the uterine endometrium — which has been prepared by the progesterone-driven secretory phase — at precisely the right developmental stage for implantation. Ectopic implantation occurs when this transport is impaired: the blastocyst is delayed, misdirected, or structurally prevented from entering the uterine cavity, and implants in the first hospitable tissue it encounters — most often the tubal mucosa. Once implanted outside the uterus, the invading trophoblast follows its programmed behaviour: it erodes blood vessels, anchors itself to the surrounding tissue, and expands — until the containing structure, whether tubal wall or uterine cornua or ovarian stroma, can no longer accommodate the growing mass and ruptures. The resulting haemorrhage can be life-threatening within minutes. The site of implantation determines the timeline to rupture and the severity of haemorrhage when it occurs.

Sites of ectopic implantation and their clinical significance:

• Ampullary (~70%): the widest tubal segment; most common site; the tube accommodates the growing conceptus longest before rupture; tends to present as 'tubal abortion' (extrusion of the ectopic through the fimbrial end) rather than tubal rupture; usually presents at 6–8 weeks
• Isthmic (~12%): narrow segment; least space for growth; tends to rupture EARLY, often at 6–7 weeks, with acute haemorrhage
• Fimbrial (~11%): near the fimbrial end; may present as tubal abortion
• Cornual/interstitial (~2–3%): within the intramural segment of the tube where it enters the uterus; very small percentage but MOST DANGEROUS because it lies surrounded by the myometrium with a dual blood supply from both uterine and ovarian arteries; rupture tends to occur LATER (10–14 weeks) but produces massive haemorrhage; requires different surgical approach
• Ovarian, abdominal, cervical: rare (<5% collectively); cervical ectopics may be confused with placenta praevia; abdominal ectopics can progress to advanced abdominal pregnancy
• Heterotopic pregnancy: simultaneous intrauterine and ectopic pregnancy; rare naturally (~1 in 30,000) but significantly increased with IVF/assisted reproduction (~1 in 100 or higher); critically important — the presence of an intrauterine pregnancy does NOT exclude a simultaneous ectopic

Risk factors for ectopic pregnancy:
All risk factors share the common mechanism of impairing tubal transport or causing tubal implantation:

• Previous ectopic pregnancy (strongest risk factor — 10× risk; future ectopic risk ~10–15%)
• Previous pelvic inflammatory disease / salpingitis: Chlamydia trachomatis and Neisseria gonorrhoeae damage tubal cilia and cause peritubal adhesions — single most modifiable population-level risk factor
• Tubal surgery: salpingostomy (leaves scarring), tubal ligation (increases ectopic risk if tubes fail to remain occluded)
• Intrauterine device (IUCD): IUCD protects against intrauterine pregnancy more effectively than tubal; if pregnancy occurs despite IUCD, it is more likely to be ectopic (does NOT mean IUCD causes ectopic — overall rate is reduced)
• Assisted reproduction: ovarian hyperstimulation disrupts normal tubal physiology; multiple embryo transfer increases heterotopic risk
• Cigarette smoking: impairs tubal motility (anti-oestrogenic effect on cilia)
• Congenital tubal anomalies: diverticulae, accessory ostia
• Endometriosis: peritubal involvement affects tubal function

Sites and Rupture Risk of Ectopic Pregnancy

Diagnosis and Investigation

The diagnosis of ectopic pregnancy is made by integrating the clinical presentation with two objective investigations: a quantitative serum β-hCG measurement and a transvaginal ultrasound (TVS). Used together and interpreted in sequence using the discriminatory zone principle, these two investigations can confirm or exclude ectopic pregnancy in the vast majority of stable patients. This algorithm is the standard of care in all settings with access to quantitative β-hCG assay and TVS — and it is the framework you must be able to apply at the bedside and articulate in a viva. One critical exception must be stated at the outset: when a patient presents with haemodynamic instability (tachycardia, hypotension, syncope, signs of haemoperitoneum), the diagnosis is made on clinical grounds alone. A woman in shock with a positive pregnancy test and abdominal peritonism has an ectopic until proven otherwise — she goes to the operating theatre without delay, not for TVS imaging. The investigation algorithm applies only to haemodynamically STABLE patients in whom there is time for a methodical diagnostic workup.

The β-hCG / TVS algorithm for haemodynamically stable patients:

Step 1 — Urine or serum β-hCG:
- Positive test confirms an active trophoblastic pregnancy (intrauterine or ectopic)
- A very high β-hCG (>100,000 IU/L) makes ectopic extremely unlikely — consider gestational trophoblastic disease

Step 2 — TVS:
- Identifies intrauterine gestational sac from ~4.5–5 weeks (TVS); yolk sac from ~5.5 weeks; fetal pole from ~6 weeks
- Finding: intrauterine sac with yolk sac/fetal pole → IUP confirmed; proceed to manage as intrauterine complication
- Finding: empty uterus + adnexal mass with echogenic ring ('tubal ring' sign) ± cardiac activity in adnexal mass → ectopic confirmed
- Finding: empty uterus, no definite adnexal mass → indeterminate; apply discriminatory zone

Step 3 — Discriminatory zone:
- The β-hCG threshold above which a TVS should always visualise an IUP: approximately 1,500–2,000 IU/L (TVS)
- β-hCG ABOVE discriminatory zone + empty uterus on TVS = presumed ectopic or failing IUP → manage accordingly
- β-hCG BELOW discriminatory zone + empty uterus = pregnancy of unknown location (PUL) — too early for TVS to confirm; repeat β-hCG in 48 hours

Step 4 — Serial β-hCG (48-hour repeat):
- Normal IUP: β-hCG rises ≥53% in 48 hours (practically 'doubles')
- Sub-optimal rise (<53% in 48 hours) → failing IUP or ectopic — requires further evaluation
- Declining β-hCG → most likely a failing pregnancy (spontaneous abortion); if declining slowly and there is no IUP on USG, ectopic still possible
- Rising β-hCG above discriminatory zone with persistently empty uterus → ectopic until proven otherwise; proceed to management

Additional investigations:
- Full blood count: haemoglobin and white cell count; eosinophilia may be present with haemoperitoneum
- Blood group and cross-match: in any haemodynamically unstable patient
- Serum progesterone: <5 ng/mL suggests non-viable pregnancy; does not distinguish site
- Posterior culdocentesis: rarely performed now (TVS has replaced it); aspiration of non-clotting blood from the pouch of Douglas confirms haemoperitoneum
- Diagnostic laparoscopy: the definitive diagnostic and therapeutic procedure when β-hCG/TVS are inconclusive and clinical suspicion remains

Diagnostic Algorithm for Suspected Ectopic Pregnancy