Ectopic Pregnancy: What Goes Wrong When Implantation Happens Outside the Uterus
Imagine someone arriving at an early pregnancy assessment unit with a positive pregnancy test, light vaginal bleeding and pain low on one side of their abdomen. They are talking comfortably and their blood pressure is normal. They ask whether they might be having a miscarriage. That is one possibility, but there is another diagnosis the team must consider early: ectopic pregnancy.
An ectopic pregnancy occurs when a pregnancy implants outside the normal uterine cavity. Most ectopic pregnancies develop within a fallopian tube. The concern is not simply that the pregnancy is in the wrong place. As pregnancy tissue grows, it can damage the tube and nearby blood vessels, sometimes leading to dangerous internal bleeding. Someone may look relatively well at first, so the history and any change in their condition matter as much as a single set of observations.
What happens when implantation occurs in the fallopian tube?
To understand the problem, follow the early embryo's normal journey. Fertilisation usually happens in the wider part of the fallopian tube, called the ampulla. The embryo then travels towards the uterus, where it would normally implant in the endometrium, the lining prepared to support a pregnancy. The uterus can enlarge as a pregnancy develops; the fallopian tube is a much narrower structure and is not built to accommodate that growth.
In a tubal ectopic pregnancy, implantation begins before the embryo reaches the uterine cavity. Cells that will become part of the placenta, called trophoblasts, normally invade nearby tissue to establish a blood supply. That process is necessary in the right location. Inside a fallopian tube, however, it can erode the tubal wall and its blood vessels.
Bleeding can begin before the tube ruptures. If the tube does rupture, blood may collect rapidly within the abdominal cavity. This is why the amount of vaginal bleeding can be misleading: some of the most serious bleeding may be happening internally, where it cannot be seen. It also explains why a person with mild symptoms earlier in the day can become acutely unwell.
Most tubal ectopic pregnancies occur in the ampullary part of the tube, although implantation can happen elsewhere in the tube or, more rarely, at other sites. Where implantation takes place affects the surrounding structures and the potential risks. The illustration below shows different sites, but the most useful starting point for a student nurse is understanding the difference between an intrauterine pregnancy and one growing in the tube.
You may hear about risk factors such as a previous ectopic pregnancy, earlier pelvic infection, tubal surgery, smoking or assisted conception. These matter because infection or surgery can affect the normal movement of the embryo through the tube. But many people with an ectopic pregnancy have no recognised risk factor. A reassuring history should never be used on its own to rule the condition out.
Why the symptoms can be easy to underestimate
Return to the patient with one-sided pain and light bleeding. They may describe a missed period, abdominal discomfort or bleeding that seems different from their usual period. Not everyone has the familiar combination of missed period, pain and bleeding. Some have very few symptoms, while others describe bowel discomfort, dizziness or feeling faint. Pregnancy is not always suspected at first, particularly if periods are irregular or contraception has been used.
One symptom worth understanding properly is shoulder-tip pain. Blood in the abdominal cavity can irritate the diaphragm. The phrenic nerve carries sensory information from the diaphragm, and the brain may interpret that irritation as pain at the shoulder tip. In a person with a possible ectopic pregnancy, shoulder-tip pain can therefore signal internal bleeding rather than a problem with the shoulder itself.
Increasing abdominal pain, shoulder-tip pain, pallor, a fast pulse, dizziness, fainting, low blood pressure or collapse can raise concern about significant bleeding. These symptoms need urgent assessment. A normal blood pressure early on is not proof that all is well: the body can compensate for blood loss for a time before hypotension becomes obvious.
From a nursing perspective, the priority is to recognise deterioration and escalate without delay. Record the symptoms and their progression, take and repeat appropriate observations, and alert the senior team if the patient's condition changes. If rupture or haemodynamic instability is suspected, emergency assessment and resuscitation take priority over waiting for a routine blood result or the next scheduled scan. Follow the local emergency pathway.
What ultrasound and pregnancy hormones can tell us
In an early pregnancy assessment unit, transvaginal ultrasound is usually the most useful scan for establishing where a pregnancy is developing. The team may see a pregnancy within the uterus, signs suggesting an ectopic pregnancy, or findings that do not yet identify the location. A transabdominal scan may be offered when an internal scan is declined or unsuitable, but its limitations need to be explained.
The image above shows an ultrasound appearance that can be associated with a tubal ectopic pregnancy. Not every ectopic pregnancy looks this obvious. Sometimes the pregnancy is too early or too small to locate. When a pregnancy test is positive but no pregnancy is identified inside or outside the uterus, clinicians call this a pregnancy of unknown location (PUL).
A PUL is not the same as a confirmed ectopic pregnancy. It may turn out to be a very early pregnancy inside the uterus, a pregnancy that is not continuing, or an ectopic pregnancy. The important point is that the location has not yet been established, so the person needs appropriate follow-up and clear advice about what to do if symptoms change.
You will often see a blood test for human chorionic gonadotrophin (hCG), a hormone produced by pregnancy tissue. Its level can help the team assess how a pregnancy is progressing, but it cannot show where the pregnancy has implanted. A rise or fall does not identify the location on its own. NICE recommends two serum hCG measurements taken as close as possible to 48 hours apart, but no earlier, when using them to guide PUL follow-up. Repeat imaging and the person's clinical condition remain important.
This is where nursing advice makes a real difference. Someone sent home after an inconclusive assessment needs to know when their next blood test or scan is due, how to contact the early pregnancy service and which symptoms mean they should seek help immediately. If they develop increasing pain, shoulder-tip pain, dizziness, faintness or heavy bleeding, they should not wait for the next scheduled hCG result. Symptoms take priority over a reassuring-looking number.
How treatment is chosen, and why follow-up matters
Once an ectopic pregnancy has been diagnosed, treatment depends on whether the person is stable, the amount of pain, the scan findings, their hCG level and whether reliable follow-up is possible. Some carefully selected people can be monitored, some are suitable for medicine, and others need surgery. The decision is not based on one measurement or a standard treatment for everyone.
Expectant management means monitoring a diagnosed ectopic pregnancy while it resolves without immediate medicine or surgery. NICE only recommends this as an option in selected patients who are clinically stable and pain-free, with suitable ultrasound findings and hCG levels, and who can return for follow-up. It is active monitoring, not simply sending someone home to see what happens.
Methotrexate may be offered by the specialist team for selected, unruptured ectopic pregnancies when a viable intrauterine pregnancy has been excluded and the person meets the relevant criteria. Methotrexate interferes with folate metabolism, reducing the growth of trophoblastic tissue. Treatment does not make the ectopic pregnancy disappear immediately. The person still needs monitoring because the pregnancy can persist or rupture before it resolves.
Following methotrexate, NICE recommends checking serum hCG on days 4 and 7 after treatment, then weekly until it becomes negative, with reassessment if levels plateau or rise. Patients also receive advice about side effects, medicine interactions, avoiding pregnancy for the recommended period and when to attend urgently. Understanding this helps a student nurse explain why an injection is only one part of the care plan.
Surgery may be necessary when there is significant pain, concern about rupture or internal bleeding, haemodynamic instability, particular scan or hCG findings, or an inability to return for safe follow-up. It may involve a salpingectomy, which removes the affected fallopian tube, or a salpingotomy, which removes the ectopic pregnancy while attempting to preserve the tube. The best approach depends on the clinical circumstances and future fertility considerations. After salpingotomy, hCG follow-up is especially important because pregnancy tissue may remain.
Whatever the treatment, resolution needs to be confirmed in the way agreed by the specialist team. Patients also need a clear plan for worsening symptoms, follow-up appointments and advice about future pregnancies. An earlier ectopic pregnancy increases the risk of another, so early assessment in a future pregnancy is important. NICE advises that people who have had an ectopic pregnancy can self-refer to an early pregnancy assessment service if they have early concerns in a future pregnancy.
Looking after the patient, not just the emergency
There is also the question of anti-D immunoglobulin for people who are RhD-negative. This helps prevent RhD sensitisation when it is indicated. The NICE guidance was updated in June 2026: anti-D is not offered for ectopic pregnancy or miscarriage up to and including 11 weeks and 6 days. At 12 weeks to 12 weeks and 6 days, it is offered to RhD-negative patients receiving medical or surgical management of ectopic pregnancy or miscarriage. The treating team should follow the current gestation-specific and local pathway rather than assuming everybody needs an injection.
An ectopic pregnancy can be a medical emergency, but it is also a pregnancy loss. Someone may be frightened by the possibility of internal bleeding while also trying to understand that the pregnancy cannot continue. Explain what is happening without rushing, respect privacy, avoid assumptions about how the person feels and make room for questions. Partners and families may also need information and support if the patient wants them involved.
When caring for someone after treatment, nursing observations and postoperative care remain essential, but so do their understanding of follow-up blood tests, expected recovery, warning signs and future pregnancy advice. Ask what information they have already been given, check what is still unclear, and document both the clinical assessment and the patient's concerns.
The central teaching point is this: an ectopic pregnancy can cause serious internal bleeding even when vaginal bleeding is light and early observations appear normal. Understanding the tubal anatomy makes the risk easier to recognise, and understanding the limits of ultrasound and hCG explains why careful reassessment and safety-netting are so important.
Related Bleepbook teaching: The menstrual cycle explains the normal reproductive timeline, while Adenomyosis explores another cause of pelvic pain and bleeding with different underlying anatomy.
References
NICE (2019; updated June 2026). Ectopic pregnancy and miscarriage: diagnosis and initial management (NG126). www.nice.org.uk/guidance/ng126.
NICE. Diagnosis of viable intrauterine pregnancy and of tubal ectopic pregnancy; pregnancy of unknown location. www.nice.org.uk/guidance/NG126/chapter/diagnosis-of-viable-intrauterine-pregnancy-and-of-tubal-ectopic-pregnancy.
NICE. Management of tubal ectopic pregnancy. www.nice.org.uk/guidance/ng126/chapter/management-of-tubal-ectopic-pregnancy.
NICE (2026). Anti-D immunoglobulin prophylaxis (NG126). www.nice.org.uk/guidance/ng126/chapter/anti-d-immunoglobulin-prophylaxis.
Royal College of Obstetricians and Gynaecologists. Ectopic pregnancy: patient information. www.rcog.org.uk/for-the-public/browse-our-patient-information/ectopic-pregnancy/.
NHS. Ectopic pregnancy: symptoms, diagnosis and treatment. www.nhs.uk/conditions/ectopic-pregnancy/.
The Ectopic Pregnancy Trust. Ectopic pregnancy information and support. ectopic.org.uk/.
Royal College of Obstetricians and Gynaecologists (RCOG). Pelvic inflammatory disease. www.rcog.org.uk/for-the-public/browse-our-patient-information/pelvic-inflammatory-disease/.