01OverviewDefinition, clinical context and the essential points that orientate the chapter.
PUL describes what is not visible at one scan; it does not state where the pregnancy is. It occurs when urine or serum testing confirms pregnancy but a competent transvaginal scan does not show a definite intrauterine gestational sac or an ectopic pregnancy. The scan may simply be too early, the pregnancy may already be failing, or trophoblast may be implanted outside the uterine cavity. Explain this uncertainty directly without calling the pregnancy ectopic or miscarried prematurely.
Start with physiology and symptoms. Record pain site, onset and progression, bleeding, clots or tissue, shoulder-tip pain, dizziness, collapse, gastrointestinal or urinary symptoms and pregnancy intention. Measure observations and assess abdominal tenderness, guarding and pallor. Atypical presentations are common. Previous ectopic pregnancy, tubal surgery, pelvic infection, assisted conception, pregnancy with an IUD and smoking increase risk, but about one-third of ectopic pregnancies have no recognised risk factor.
Review the ultrasound with its context. Confirm that imaging was transvaginal, performed by someone trained in early-pregnancy diagnosis, and that uterus, both adnexa and the pelvis were examined. An empty uterus alone is not an ectopic diagnosis. Likewise, a small intrauterine fluid collection can be a pseudosac. A documented earlier intrauterine pregnancy changes interpretation of an apparently complete miscarriage; without that earlier proof, an empty uterus remains a PUL until follow-up resolves it.
NICE uses two serum hCG samples as near as possible to 48 hours apart, but not sooner. hCG describes trophoblastic activity rather than anatomical location. A rise above 63% makes a developing intrauterine pregnancy likely, yet ectopic remains possible. Plan repeat transvaginal ultrasound in 7–14 days, considering an earlier scan once hCG reaches at least 1,500 IU/L. If that scan still does not show a viable intrauterine pregnancy, arrange immediate senior review.
A decline above 50% over 48 hours means the pregnancy is unlikely to continue, but its previous location may remain unknown. Provide loss support and a urine pregnancy test 14 days after the second serum result. A negative test closes follow-up in an asymptomatic patient; a positive test requires early-pregnancy review within 24 hours. Persisting symptoms override this low-risk biochemical branch.
The indeterminate middle group is a fall below 50% or rise below 63%. This includes plateauing hCG and is associated with ectopic or persisting trophoblast. NICE recommends early-pregnancy clinical review within 24 hours rather than an automatic third blood test. A senior clinician integrates symptoms, examination, hCG, scan quality, pregnancy intention and potential treatment. Serum progesterone should not be added to distinguish ectopic from intrauterine pregnancy.
Do not apply a discriminatory zone as a treatment trigger. Above a chosen hCG concentration, failure to see an intrauterine pregnancy increases concern but does not prove ectopic pregnancy; multiple gestation, timing error, scan quality and uterine pathology can change visibility. Methotrexate on the first visit is appropriate only after a definitive ectopic diagnosis and exclusion of a viable intrauterine pregnancy under NICE criteria, not simply because the uterus is empty at hCG 1,500 or 2,000.
Safe outpatient care depends on communication. Give written information that location remains unresolved, exact blood and scan appointments, a 24-hour number and emergency symptoms. Check language, transport, caring responsibilities and phone access. Ask how the patient wants a partner involved and respect confidentiality. Maintain follow-up until a definite intrauterine pregnancy, confirmed ectopic pregnancy or negative testing establishes resolution.
Key points
- Pregnancy of unknown location is an ultrasound classification: the pregnancy test is positive but transvaginal ultrasound shows neither definite intrauterine nor definite extrauterine pregnancy.
- Possible outcomes are an early viable intrauterine pregnancy, a failing intrauterine pregnancy that has not been documented, or an ectopic pregnancy; the label is not a final diagnosis.
- Assume ectopic pregnancy remains possible until location is established or follow-up demonstrates complete resolution.
- Take two serum hCG measurements as close as possible to 48 hours apart, but no earlier; use them to plan follow-up, never to assign anatomical location.
- A rise greater than 63% suggests a developing intrauterine pregnancy but does not exclude ectopic; arrange transvaginal ultrasound in 7–14 days, earlier when hCG is at least 1,500 IU/L.
- A fall greater than 50% suggests a pregnancy unlikely to continue; arrange a urine test 14 days after the second blood test and review within 24 hours if it remains positive.
- A rise below 63% or fall below 50% requires clinical review in the early-pregnancy service within 24 hours because ectopic or persisting PUL is more likely.
- Do not use serum progesterone, a single discriminatory hCG threshold or reassuring absence of risk factors to close the pathway.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Very early intrauterine pregnancy
Implantation may be normal but the gestational sac remains below ultrasound resolution, particularly with uncertain ovulation, irregular cycles or late conception.
Failing intrauterine pregnancy
An early intrauterine pregnancy may stop developing and pass before its location was ever documented, leaving positive hCG and an empty cavity.
Ectopic implantation
Trophoblast implanted in a fallopian tube or another extrauterine site produces hCG without creating a definite intrauterine gestational sac.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Sub-resolution trophoblast
Trophoblast begins hCG secretion before an intrauterine sac becomes consistently visible, creating a normal physiological interval of diagnostic uncertainty.
- 2Abnormal trophoblastic kinetics
Failing or ectopic trophoblast often rises more slowly, plateaus or falls, but considerable overlap prevents any hCG curve from determining location.
- 3Tubal invasion and rupture
Ectopic trophoblast erodes tubal tissue and vessels; bleeding can remain occult until distension or rupture causes intraperitoneal haemorrhage.
- 4Delayed hormone clearance
hCG may remain detectable for days or weeks after pregnancy tissue stops developing or passes, so biochemical resolution lags clinical events.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
No visible pregnancy with a rise above 63% over 48 hours makes developing intrauterine pregnancy likely, but requires later imaging to prove location.
A decline above 50% over 48 hours suggests a pregnancy unlikely to continue and leads to a timed urine-test closure pathway.
A plateau, rise below 63% or fall below 50% leaves greater concern for ectopic or persisting trophoblast and needs review within 24 hours.
Worsening unilateral pain, shoulder-tip pain, syncope, peritonism or haemodynamic change requires emergency action even with a low or falling hCG.
An empty uterus after bleeding is not proof of completed intrauterine loss unless an earlier scan documented the pregnancy inside the uterus.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Transvaginal ultrasoundFirst step - Why
- Search for a definite intrauterine pregnancy, adnexal ectopic features and haemoperitoneum with the most sensitive early approach.
- Interpretation and limitations
- No pregnancy seen creates a PUL, not a diagnosis of miscarriage. Offer transabdominal scanning if internal imaging is declined and explain its lower early sensitivity.
- 02
Paired quantitative serum hCG - Why
- Measure trophoblastic proliferation and select the next follow-up branch.
- Interpretation and limitations
- Take samples as close as possible to 48 hours apart but not earlier. Use >63% rise, >50% fall and indeterminate middle thresholds without assigning location.
- 03
Full blood count - Why
- Assess anaemia, bleeding impact and a baseline if operative or methotrexate management later becomes necessary.
- Interpretation and limitations
- Normal haemoglobin does not exclude acute intraperitoneal bleeding; physiology and trajectory determine urgency.
- 04
Blood group and RhD status - Why
- Prepare transfusion support and identify whether current 2026 anti-D recommendations apply at 12+0 to 12+6 weeks.
- Interpretation and limitations
- Do not offer anti-D up to 11+6 weeks for PUL, ectopic or miscarriage; gestation and management determine treatment from 12 weeks.
- 05
Renal, liver and other pre-treatment bloods - Why
- Assess suitability only when methotrexate or surgery is being considered after diagnosis.
- Interpretation and limitations
- These tests do not locate a pregnancy. Abnormalities may contraindicate methotrexate or change anaesthetic planning.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Viable early intrauterine pregnancy
Normal implantation may simply precede ultrasound visibility and will later be demonstrated by appropriately timed repeat imaging.
Completed miscarriage
Bleeding may have expelled an intrauterine pregnancy, but this diagnosis is secure only when earlier imaging proved its location or follow-up excludes ectopic.
Tubal ectopic pregnancy
Pain, abnormal hCG or adnexal findings may develop later, and rupture remains possible even while hCG falls.
Non-tubal ectopic pregnancy
Cervical, caesarean-scar, interstitial, ovarian or abdominal implantation can be missed if scanning focuses only on the fallopian tubes.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01Immediate dangerTreat possible rupture firstFirst stepA patient with PUL develops haemodynamic change, severe pain, peritonism, syncope or significant bleeding.+
- 1Activate ABCDE care, two large-bore cannulas, urgent bloods and group-and-save or crossmatch, analgesia and senior gynaecology and anaesthetic support.
- 2DefinitiveUse bedside or urgent formal imaging only if it does not delay definitive control; free fluid plus shock is enough to prioritise emergency surgery.
- 3Continue resuscitation, blood-product support and operative preparation while communicating uncertainty and obtaining consent to the extent the emergency permits.
02Stable first assessmentCreate the 48-hour planThe patient is clinically stable and ultrasound meets the definition of PUL.+
- 1Review symptoms, observations, examination, risk factors and scan quality and obtain the first quantitative hCG without using it to name the location.
- 2Book the second hCG as near as possible to 48 hours later, confirm reliable contact and give written emergency symptoms and a 24-hour service number.
- 3Document pregnancy intention, communication needs and exact responsibility for checking results so a missed sample or non-attendance triggers active follow-up.
03Rising hCGImage to prove locationSerum hCG increases by more than 63% over 48 hours.+
- 1Explain that a developing intrauterine pregnancy is likely but ectopic pregnancy is not excluded and symptoms still require immediate reassessment.
- 2Arrange transvaginal ultrasound in 7–14 days, considering an earlier scan when hCG is at least 1,500 IU/L.
- 3If a viable intrauterine pregnancy is not demonstrated, obtain immediate senior gynaecology review rather than repeatedly labelling the trend reassuring.
04Falling or indeterminate hCGClose only after resolutionThe 48-hour hCG falls or changes less than the reassuring rise threshold.+
- 1For a fall above 50%, provide support and a urine pregnancy test 14 days after the second blood result, with review within 24 hours if positive.
- 2For a fall below 50% or rise below 63%, arrange early-pregnancy clinical review within 24 hours and senior-directed further testing or treatment.
- 3EscalationIn either branch, escalate immediately for new pain, collapse or bleeding because biochemical decline does not eliminate rupture risk.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Ectopic rupture
Unrecognised extrauterine pregnancy can rupture and cause rapid intraperitoneal bleeding, shock, emergency surgery, transfusion or death.
Inadvertent viable-pregnancy treatment
Using hCG alone to diagnose ectopic can expose an early viable intrauterine pregnancy to methotrexate or surgery.
Persistent trophoblast
Plateauing hCG may represent persisting PUL that requires further imaging, uterine assessment, methotrexate or surgery under specialist care.
Psychological harm
Repeated tests, ambiguous language and prolonged uncertainty can intensify anxiety, grief and loss of trust even when the pregnancy resolves physically.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Track every paired hCG, repeat scan and urine test to a named clinician until pregnancy location or complete biochemical resolution is documented.
- Contact a patient who misses testing while location is unknown and address language, transport, phone or safeguarding barriers rather than recording non-attendance only.
- Reassess symptoms at every contact and instruct the patient that new pain, dizziness, shoulder-tip pain, collapse or heavier bleeding overrides scheduled follow-up.
- Avoid repeated hCG tests without a senior decision; each result must lead to a defined scan, review, treatment or closure action.
- Offer support for likely pregnancy loss even while location remains uncertain and ask whether future pregnancy or contraception counselling is wanted after resolution.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
PUL is a holding diagnosis
It protects against premature conclusions while obligating follow-up; it should disappear from the record only when location or resolution is established.
The uterus can be empty twice
It may be genuinely too early or the pregnancy may be ectopic or already failing, so the same image can lead to very different outcomes.
hCG measures activity, not geography
Even a textbook rise cannot place trophoblast inside the uterus, and an abnormal trend cannot reveal whether tissue is tubal or intrauterine.
Clinical change resets the pathway
A new symptom invalidates a previously reassuring outpatient plan and requires fresh assessment independent of the next booked blood test.
Complete miscarriage requires provenance
Without a prior confirmed intrauterine pregnancy, disappearance after bleeding remains an unresolved location problem until hCG follow-up finishes.
11Common pitfallsFrequent interpretation and management errors.
- 01
Calling an empty uterus at one scan a miscarriage or ectopic pregnancy instead of a pregnancy of unknown location.
- 02
Using a single hCG value or discriminatory threshold to diagnose location or give methotrexate.
- 03
Reassuring from a rise above 63% without arranging ultrasound confirmation of location.
- 04
Assuming a falling hCG eliminates rupture risk and ignoring new pain or haemodynamic change.
- 05
Adding serum progesterone to distinguish ectopic from viable intrauterine pregnancy despite NICE advice.
- 06
Discharging without booked follow-up, written emergency advice, a 24-hour contact and active tracking of non-attendance.