extrauterine pregnancy
Meaning of extrauterine pregnancy: The rarer implantation sites are the difficult ones, being harder to see on a scan and behaving differently from a pregnancy in the tube.
Definition of extrauterine pregnancy
Extrauterine pregnancy is a pregnancy in which the fertilized egg implants and develops outside the cavity of the uterus rather than in the uterine lining. It is another name for ectopic pregnancy. The great majority occur within a fallopian tube, with the remainder scattered across a handful of much rarer sites.
Why does the egg implant in the wrong place?
Fertilization normally happens in the outer part of a fallopian tube, and the developing embryo is then carried toward the uterus across several days by fine beating hairs lining the tube and by gentle muscular waves. Implantation occurs once the embryo reaches a particular stage, and the timing is set so that stage coincides with arrival in the uterus. Anything slowing or obstructing the journey lets the stage arrive first, and the embryo implants wherever it happens to be. Scarring from previous infection, damage to the hair-like lining, earlier surgery on the tube, and endometriosis all interfere with transport in exactly this way, which explains why the tube is by far the most common site.
Which sites are involved?
| Site | Why it matters |
|---|---|
| Outer portion of the tube | The commonest location by a wide margin |
| The segment of tube within the uterine wall | Surrounded by muscle, so it can grow larger before tearing, and bleeds heavily when it does |
| Ovary | Rare, and hard to tell apart from other ovarian findings |
| The cervix | Rare, with a rich blood supply making bleeding difficult to control |
| Abdominal cavity | Rare, sometimes found late because there is more room to grow |
| A previous cesarean scar | Uncommon, and increasingly recognized |
How is it found?
Presentation varies more than any summary suggests. One-sided pelvic or abdominal pain with vaginal bleeding after a missed period is the classic combination, yet pain can be central or absent, bleeding is sometimes mistaken for a light period, and some are found on an early scan before any symptom appears at all. Identification combines a pregnancy test, measurement of the pregnancy hormone in blood repeated after a short interval to see how the level is behaving, and ultrasound. A scan performed through the vagina gives a closer view of the uterus and the structures beside it than one performed through the abdominal wall. The finding that raises the strongest suspicion is a hormone level high enough that a pregnancy inside the uterus should be visible, paired with an empty uterine cavity. Ectopic pregnancy is the term used more often in practice, and the two are interchangeable.
Also known as
Used in a sentence
Ultrasound was performed to evaluate for a suspected extrauterine pregnancy after an abnormal hormone level was noted.
Good to know
Most extrauterine pregnancies occur within a fallopian tube, but rarer locations including the ovary, the cervix and the abdominal cavity are evaluated differently and can be considerably harder to identify on initial imaging.
Word origin
Where “extrauterine pregnancy” comes from
Formed from extra-, Latin for outside, and uterine, from uterus, together describing a pregnancy located outside the uterus.