Causes and Risk Factors of Ectopic Pregnancy

1. Prior Ectopic Pregnancy (Strongest Risk Factor)

• A previous ectopic pregnancy is the single most important risk factor.
• Recurrence risk: ~10-15% after the first ectopic, rising to ~30% after a second.
• The elevated recurrence stems from the original predisposing condition plus additional tubal damage from the ectopic itself and its treatment.
• Berek & Novak's Gynecology, p. 1754

2. Pelvic Inflammatory Disease (PID) / Salpingitis

• The rate of ectopic pregnancy in women with a known history of PID is 6-10 times higher than in those without.
• PID (usually caused by Chlamydia trachomatis or Neisseria gonorrhoeae) causes intense tubal inflammation, filling tubes with bacteria, white cells, and exudate.
• During healing, the delicate tubal mucosa is permanently scarred, partially or completely blocking the lumen and fimbriated end with scar tissue.
• Tubal inflammation is present in up to 90% of ectopic pregnancies, with causes including PID, tubal endometriosis, and salpingitis isthmica nodosa.
• Textbook of Family Medicine 9e, p. 492; Berek & Novak's Gynecology, p. 1754

3. Tubal Surgery

• Any prior surgery on the fallopian tubes significantly increases ectopic risk.
• Includes: tubal ligation (sterilization), salpingostomy, salpingoplasty, fimbrioplasty, and surgical treatment of a previous ectopic pregnancy.
• Mechanism: adhesions, scarring, and altered tubal anatomy disrupt normal ovum transport.
• Berek & Novak's Gynecology; Roberts and Hedges' Clinical Procedures in Emergency Medicine

4. Intrauterine Contraceptive Device (IUD)

• IUDs are highly effective overall (annual failure rate <0.1%), but the rare pregnancies that do occur while using an IUD are disproportionately ectopic.
• Associated with approximately a 2-fold increase in ectopic pregnancy risk.
• Progestin-bearing IUDs specifically are associated with ectopic risk.
• Robbins & Kumar Basic Pathology; Berek & Novak's Gynecology, p. 1754

5. Assisted Reproductive Technologies (ART)

• In vitro fertilization (IVF) and ovulation induction are linked to increased ectopic risk, though the exact mechanism is unclear since the tube is technically bypassed during embryo transfer.
• The underlying infertility conditions requiring ART (e.g., tubal disease) likely contribute.
• The increasing use of ART is thought to partly explain the rising reported incidence of ectopic pregnancy.
• Textbook of Family Medicine 9e; Tintinalli's Emergency Medicine

6. Endometriosis

• Endometriosis involving the fallopian tubes causes inflammation, adhesions, and mechanical obstruction of the tubal lumen.
• Can impair the smooth muscle contractions and ciliary action required for ovum transport.
• Robbins & Kumar Basic Pathology, p. 909; Berek & Novak's Gynecology

7. Peritubal and Pelvic Adhesions

• Adhesions from previous pelvic or abdominal surgery (e.g., appendectomy, ovarian cystectomy, cesarean section) can distort tubal anatomy and impair transport.
• Adhesive disease can also result from prior peritonitis.
• Robbins & Kumar Basic Pathology, p. 909

8. Intrauterine Tumors / Uterine Anomalies

• Submucous fibroids or polyps near the tubal ostia can obstruct entry into the uterine cavity.
• Congenital uterine anomalies may also contribute.
• Robbins & Kumar Basic Pathology, p. 909

9. Cigarette Smoking

• Smoking is associated with ectopic pregnancy, likely by altering embryo tubal transport - possibly through effects on tubal ciliary function and smooth muscle motility.
• This is considered a moderate/weak independent risk factor.
• Tintinalli's Emergency Medicine; Berek & Novak's Gynecology

10. Advanced Maternal Age (35-44 years)

• Age-related decline in tubal function (ciliary beat frequency, smooth muscle activity) slows ovum transport.
• Tintinalli's Emergency Medicine

11. Salpingitis Isthmica Nodosa (SIN)

• A condition characterized by nodular thickening of the tubal isthmus with diverticula lined by tubal epithelium burrowing into the myosalpinx.
• Strongly associated with ectopic pregnancy and infertility; found in up to 90% of ectopic cases in some series.
• Berek & Novak's Gynecology

12. Hormonal Factors

• Elevated estradiol or progesterone levels (e.g., from ART stimulation protocols) can inhibit tubal peristalsis and smooth muscle contractions that propel the embryo toward the uterus.
• Progestin-only contraceptive failures are associated with ectopic implantation.
• Tintinalli's Emergency Medicine

13. Multiple Lifetime Sexual Partners

• Weakly associated, likely as a proxy for increased STI exposure and subclinical PID.
• Berek & Novak's Gynecology

14. Prior Induced Abortion

• Prior pharmacologically or surgically induced abortion is listed as a risk factor, possibly due to subclinical infection or uterine instrumentation causing adhesions.
• Tintinalli's Emergency Medicine

Special Sites and Their Mechanisms

Summary Table of Risk Factors