Ectopic pregnancy: when and how it shows on ultrasound
An ectopic pregnancy occurs in about one pregnancy in a hundred and is the leading cause of death in the first trimester. That is why nobody suggests waiting when the test is positive and the uterus is empty. Below: what the scan shows, why one scan is rarely enough, and the signs that mean hospital rather than an appointment.
What an ectopic pregnancy is
It is a pregnancy that has implanted outside the uterine cavity. In more than 90 per cent of cases in the fallopian tube, less often in the ovary, the cervix, a caesarean scar or the abdominal cavity. Such a pregnancy cannot develop, and it cannot be moved into the uterus.
The danger is that the growing embryo stretches the tube until it ruptures, causing bleeding into the abdomen. The whole point of the workup is to find the pregnancy before that happens.
Symptoms and when they appear
Most often between 6 and 8 weeks, sometimes before a woman realises she is pregnant at all. The usual picture:
- one-sided lower abdominal pain, dull at first and then sharper;
- spotting or bleeding, usually scant and dark, unlike a period;
- a missed period and a positive test;
- pain on passing urine or stool, a feeling of pressure.
Shoulder-tip pain together with dizziness already means bleeding into the abdomen: blood irritates the diaphragm, which refers pain to the shoulder. That situation will not wait.
What the scan shows, and from when
A transvaginal scan can usually identify an ectopic pregnancy from 5–6 weeks. The picture is read as a whole, not from any single sign:
| What is assessed | What it means |
|---|---|
| An empty uterine cavity | With hCG above the threshold and an empty uterus, the pregnancy is somewhere else until proven otherwise |
| A mass beside the ovary | A ring with a bright rim next to the ovary — the commonest appearance of a tubal pregnancy; sometimes a yolk sac or embryo can be seen inside it |
| Free fluid behind the uterus | A small amount can be normal; a large amount of dense-looking fluid suggests bleeding |
| Pseudogestational sac | Fluid in the uterine cavity that looks like a gestational sac but has no yolk sac — a trap specific to ectopic pregnancy |
Finding a normal pregnancy inside the uterus all but rules an ectopic out — except after IVF, where a pregnancy in both places at once is rare but possible.
What hCG adds
A scan alone does not always answer the question, so it is read together with a blood beta-hCG. Two things matter.
The threshold. Above a certain hCG level a normal intrauterine pregnancy should already be visible. Current guidance sets that threshold high, around 3500 IU/l, precisely to avoid the opposite error — calling ectopic a pregnancy that is simply younger than the dates suggested.
The trend. In a normal early pregnancy hCG rises by at least half over 48 hours. A slower rise, no rise, or a slow fall all point to an abnormal pregnancy — but on their own they do not distinguish an ectopic from a miscarriage.
Pregnancy of unknown location
That is the name for a positive test, an empty uterus, and nothing visible outside it either. It is not a diagnosis but a stage: in about half of these cases the pregnancy turns out to be normal and simply early.
Management means repeating hCG every 48 hours and rescanning in a few days, with instructions to come in immediately if pain or bleeding appears. This is not delay — it is the only way to avoid treating a pregnancy that will turn out to be normal.
How it is treated
The choice depends on how the patient is, the hCG level, the size of the mass and whether there is bleeding into the abdomen:
- Expectant management — with a low and falling hCG and no symptoms: some ectopic pregnancies resolve on their own, under close monitoring.
- Methotrexate — an injection that stops the pregnancy tissue growing. An option when the patient is stable and the criteria are met.
- Surgery — laparoscopy, sometimes removing the tube. Necessary if the tube has ruptured, if there is bleeding, or if conservative treatment fails.
Women who are Rh negative are given anti-D immunoglobulin.
What raises the risk
Half the women who have an ectopic pregnancy have none of these — their presence changes how closely you watch, not the diagnosis.
- a previous ectopic pregnancy;
- previous pelvic inflammatory disease, especially chlamydial;
- tubal surgery, including sterilisation;
- endometriosis;
- pregnancy after IVF or ovulation induction;
- conceiving with an IUD in place;
- smoking.
Short answers
Can an ectopic pregnancy be seen on ultrasound?
Yes, usually from 5–6 weeks on a transvaginal scan: an empty uterine cavity with hCG above the threshold, a mass beside the ovary, sometimes free fluid. The diagnosis rests on the scan together with hCG, rarely on one scan alone.
Does an ectopic pregnancy always hurt?
No. Early on it may cause no symptoms at all, or only light spotting. Pain usually starts between 6 and 8 weeks and builds.
What does an empty uterus with a positive test mean?
Three possibilities: the pregnancy is too early, it is a pregnancy of unknown location, or it is ectopic. They are told apart by repeating hCG every 48 hours and rescanning.
Can you conceive after an ectopic pregnancy?
Yes. Most women go on to have a normal pregnancy, including after one tube has been removed. The risk of a repeat is higher, though, so the next pregnancy is confirmed by ultrasound early, at about 6 weeks.
This text describes the general picture and does not replace a consultation. Timings and indications differ from woman to woman and are decided at the appointment, from your history and test results.