Ectopic pregnancy
- Lesion
When an embryo implants outside the uterus, usually in the tube, the tube cannot stretch; it bursts and bleeds into the abdomen.
What it is
Ectopic pregnancy is implantation outside the endometrial cavity, and more than nine in ten occur in the fallopian tube. Anything that slows the embryo's passage, above all scarring from previous salpingitis, raises the risk. The trophoblast invades the thin tubal wall and its vessels, so the tube distends with blood and eventually ruptures, causing a hemoperitoneum that can be fatal. Meanwhile the endometrium becomes decidualised without villi, often with the Arias-Stella reaction.
Structure
- The tube is swollen, purple and filled with blood clot (haematosalpinx), with a rupture site in the wall.
- Chorionic villi and implantation-site trophoblast invade the muscularis and vessels; an embryo may or may not be seen.
- Tubal abortion: the pregnancy is extruded through the fimbriated end with bleeding into the pelvis.
Step by step
- Damage to tubal cilia and folds, usually from past infection, slows transport of the fertilised ovum.
- The blastocyst implants in the tubal mucosa.
- Without a decidua to limit it, the trophoblast invades deeply into the thin wall and its arteries.
- Blood accumulates in the lumen and wall, distending the tube.
- The tube ruptures, causing intraperitoneal haemorrhage, or the pregnancy is aborted through the fimbria.
Clinical notes
- Classic triad: amenorrhea, abdominal pain and vaginal bleeding; ruptured ectopic causes shock with hemoperitoneum.
- hCG rises more slowly than normal and transvaginal ultrasound shows no intrauterine pregnancy at an hCG level at which one should be visible.
- Ectopic pregnancy remains an important cause of maternal death in the first trimester.
Test yourself
Think of the answer, then tap the question to see it.
What is the most important risk factor for tubal ectopic pregnancy?
Previous pelvic inflammatory disease with chronic salpingitis that has scarred the tube.
What is the Arias-Stella reaction?
Enlarged, hyperchromatic, atypical-looking nuclei in endometrial glands caused by pregnancy hormones; it occurs in normal and ectopic pregnancy and is not malignant.
Why does a tubal pregnancy rupture?
The tube has no decidua and a thin wall, so the trophoblast invades its vessels and the wall gives way as blood accumulates.
Elsewhere in DurgiPedia
- Uterine tube
- Trophoblast and hCG; gestational trophoblastic disease
- The placenta and pregnancy hormones
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Ectopic Pregnancy (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.