Pregnancy of unknown location (PUL)

Definition

Definition and possible outcomes

• A pregnancy of unknown location (PUL) is present when there is a positive pregnancy test and a measurable beta-hCG level, but an ultrasound scan shows no intra- or extrauterine gestational sac is visible.
• A rare course is a persistent PUL, in which the location remains unclear in the further course.

• A pregnancy of unknown location (PUL) is present when the pregnancy test is positive but transvaginal ultrasound cannot locate the pregnancy either inside or outside the uterus.
• It is a classification, not a diagnosis.

Classification

• Final outcomes are: intrauterine pregnancy (viable or non-viable), failed pregnancy of unknown location (failed PUL), ectopic pregnancy and persisting PUL.
• A persisting PUL is commonly defined as more than three serial hCG values changing by less than 15% while the pregnancy still cannot be located on ultrasound.

Occurrence & epidemiology

Epidemiology

• The proportion of early pregnancies initially classified as PUL ranges from 8% to 42% between units; a low proportion indicates good quality of early pregnancy ultrasound.
• Most PULs end as a failed PUL (47–70%), fewer as an intrauterine pregnancy (17–41%) or an ectopic pregnancy (8–16%).

Clinical features

Clinical features and complications

• Many patients present with lower abdominal pain or vaginal bleeding; however, these symptoms do not identify which PULs carry a high risk of complications.

Diagnosis

• Single hCG measurements are of little value; the key parameter is the hCG ratio, the 48-hour value divided by the initial value.
• A ratio below 0.87 (a fall of at least 13%) points to a failed PUL, a ratio above 1.66 to an intrauterine pregnancy; values in between are more consistent with an ectopic pregnancy or persisting PUL.
• A serum progesterone of 10 nmol/L or less is associated with a failing pregnancy; progesterone predicts viability but not location.
• A single hCG discriminatory zone is not suitable for presuming an ectopic pregnancy.

Keep learning in the app

Further reading (selection)

1. Womens Health (Lond) 2017: Factors to consider in pregnancy of unknown location (PMC, open access)
2. MSD Manual Professional Edition: Ectopic Pregnancy (Pregnancy of Unknown Location)
3. DocCheck Flexikon, Extrauteringravidität

Cross-references