A 32-year-old woman with a history of pelvic inflammatory disease presents with a positive urine pregnancy test, right lower abdominal pain, and hemodynamic instability. Serum β-hCG is elevated. What is the most common cause of ectopic pregnancy?

Explanation

## Most Common Cause of Ectopic Pregnancy **Key Point:** Salpingitis and pelvic inflammatory disease (PID) are the most common causes of ectopic pregnancy, accounting for approximately 30–40% of cases. Tubal damage from infection leads to impaired ciliary function and stricture formation, delaying embryo transport. ### Causes of Ectopic Pregnancy: Frequency and Mechanism | Cause | Frequency | Mechanism | |-------|-----------|----------| | **Salpingitis / PID** | **30–40%** | **Tubal scarring, strictures, impaired ciliary function** | | Endometriosis | 10–15% | Tubal distortion, altered peristalsis | | IUD use | 5–10% | Altered tubal motility, inflammatory response | | Previous tubal surgery | 5–10% | Stricture, adhesions | | Previous uterine curettage | 2–5% | Rare; mechanism unclear | | Tubal anomalies | 2–5% | Diverticula, strictures | | Unexplained | 20–30% | No identifiable risk factor | **High-Yield:** PID causes tubal damage through: 1. Acute inflammation → mucosal edema and exudate 2. Chronic inflammation → fibrosis, stricture formation, and partial occlusion 3. Loss of ciliary epithelium → impaired embryo transport 4. Altered tubal peristalsis → delayed passage of blastocyst ### Clinical Pearl **Clinical Pearl:** A history of PID (especially recurrent or inadequately treated) is the single strongest risk factor for ectopic pregnancy. Chlamydial and gonococcal infections carry the highest risk because they cause severe tubal damage. **Mnemonic:** **SEITU** — **S**alpingitis (most common), **E**ndometriosis, **I**UD, **T**ubal surgery, **U**terine curettage. ### Why Other Causes Are Less Common - **Endometriosis (~10–15%):** Tubal distortion and altered peristalsis; second most common identifiable cause, but less frequent than PID. - **IUD use (~5–10%):** Alters tubal motility and creates a local inflammatory environment; however, modern IUDs have lower risk than older devices. - **Previous uterine curettage (~2–5%):** Rare cause; mechanism is unclear and may involve Asherman's syndrome or tubal involvement, but it is not a primary risk factor. ### Pathophysiology of PID-Related Ectopic Pregnancy ```mermaid flowchart TD A[Chlamydia/Gonorrhea infection]:::outcome --> B[Acute salpingitis]:::outcome B --> C{Adequately treated?}:::decision C -->|No| D[Chronic inflammation]:::action C -->|Yes| E[Resolution]:::action D --> F[Tubal fibrosis & stricture]:::outcome F --> G[Impaired embryo transport]:::outcome G --> H[Blastocyst implants in tube]:::urgent H --> I[Ectopic pregnancy]:::urgent E --> J[Normal tubal function]:::outcome ``` [cite:Jeffcoate's Principles of Gynaecology 8e Ch 8]