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PH-RO03

Ectopic pregnancy

How damage to the uterine tube delays the embryo so that it implants outside the uterine cavity, why the tube cannot contain the pregnancy, and how rupture causes internal bleeding.

By the end, you can

  • Describe fertilisation in the ampulla, transport along the uterine tube and normal implantation.
  • Explain how tubal damage and other risk factors lead to implantation outside the uterine cavity.
  • Name the sites of ectopic implantation and their relative frequency.
  • Explain why a tubal pregnancy causes slow-rising hCG, vaginal bleeding and pain, and why it can rupture.
  • Relate haemoperitoneum to shoulder-tip pain, free fluid in the recto-uterine pouch and shock.
  • Recognise the classic tissue findings, key hCG values and tests of ectopic pregnancy, and explain how each main treatment acts on its mechanism.

What it is

An ectopic pregnancy is one that implants outside the endometrial lining of the uterine cavity. More than nine in ten are in the uterine tube, most in the ampulla; the rest implant in the interstitial part of the tube, the ovary, the cervix, a caesarean-section scar or the abdominal cavity.

4 types to tell apart
Tubal (ampullary, isthmic, fimbrial)
The great majority. The narrow isthmus tends to rupture earlier than the wider ampulla.
Interstitial
In the part of the tube that runs through the uterine wall. Surrounded by myometrium, it can grow for longer and then bleed heavily.
Non-tubal
Ovarian, cervical, caesarean-scar and abdominal pregnancies; rare, and often with a high risk of bleeding.
Heterotopic
An intrauterine and an ectopic pregnancy at the same time; rare, but more common after assisted conception.

US spelling: caesarean → cesarean, oestradiol → estradiol.

Normal function

Fertilisation, transport and implantation

After ovulation, the sweep the egg into the of the uterine tube. Fertilisation usually happens in the wide , within about a day of ovulation.

The tube then carries the embryo towards the uterus over about three to four days. Beating cilia on its lining and waves of contraction in its smooth muscle move it through the narrow , under the influence of oestradiol and progesterone. Meanwhile the embryo divides and reaches the uterine cavity as a morula.

By about day 5 it is a blastocyst. It hatches from its coat and, around days 6–7, its outer trophoblast attaches to and invades the endometrium, usually high on the back wall of the . Under progesterone the endometrium has become decidua: a thick, nutrient-rich lining that both supports and limits the invading trophoblast.

Point to it on the model