Pregnancy of Unknown Location (PUL)
Pregnancy of unknown location (PUL) describes the scenario where a person has a positive pregnancy test, but the ultrasound does not show either an intrauterine pregnancy or an extrauterine pregnancy. It is not a final diagnosis, but a temporary clinical classification while further assessment is arranged. The key concern is excluding an ectopic pregnancy.
This updated UKMLA guide to PUL is based on NICE NG126, which covers definition, causes, referral criteria, work-up and management approach.
Definition
Pregnancy of unknown location refers to:
- Positive pregnancy test, BUT
- TVUS does NOT demonstrate an intrauterine or extrauterine pregnancy
Pregnancy of unknown location is not a final diagnosis, but a temporary clinical classification while a definitive diagnosis on the pregnancy type / outcome can be made.
Causes
There are 3 main causes to consider:
- Very early intrauterine pregnancy (not yet visible on ultrasound)
- Ectopic pregnancy
- Miscarriage
The main concern of pregnancy of unknown location is that the person could have an ectopic pregnancy.
Referral Criteria / Urgent Escalation
| Scenario | Referral recommendations | Rationale |
|---|---|---|
+ve Pregnancy test PLUS any of the following:
|
Immediate referral to early pregnancy assessment service (or out-of-hours gynaecology service) | Possible ectopic pregnancy |
Vaginal bleeding PLUS any of the following:
|
Refer to early pregnancy assessment service (or out-of-hours gynaecology service)
Urgency depends on clinical judgement |
Possible ectopic pregnancy or miscarriage |
Offer expectant management (instead of referring immediately) if ALL the following apply (low risk of ectopic pregnancy):
- <6 weeks of gestation
- PAINLESS bleeding
- No risk factors (e.g. previous ectopic pregnancy)
Expectant management involves:
- Safety netting – to return if bleeding continues or pain develops
- Repeat urine pregnancy test after 7-10 days, and return if +ve
Work-Up and Management
Perform serial hCG measurement
- Take TWO measurements at least 48 hours apart
- The second sample should be taken as close to 48 hours as possible (i.e. ideally immediately after 48 hours, or as soon as possible thereafter)
Interpretation:
| Change in hCG after 48 hours | Likely explanation | Recommended next steps |
|---|---|---|
| Increase >63%* | Early viable intrauterine pregnancy | Perform TVUS in 7-14 days (or earlier if hCG >1,500)
|
| Decrease >50% | Miscarriage / failing pregnancy | Perform a urine pregnancy test in 14 days
|
| Increase <63% OR decrease <50% | Ectopic pregnancy | Attend early pregnancy assessment service within 24 hours
|
*A normal early intrauterine pregnancy typically roughly doubles its hCG level every 48 hours, which corresponds approximately to a >63% rise over 48 hours. This can be a useful simplified way to remember the threshold.
Serial hCG trends after 48 hours are NOT diagnostic on their own. They are simply used to guide triage, risk stratification, and further investigation.