Pregnancy of Unknown Location

What is a pregnancy of unknown location?

A pregnancy of unknown location, often referred to by healthcare professionals as a “PUL” is a diagnosis given to a patient when she has a positive pregnancy test but an ultrasound scan has not been able to visualise the pregnancy. Women may also be told that their scan is inconclusive. A lot of the time this is simply because they have presented to the clinic extremely early in their pregnancy and the embryo and even the sac is simply too tiny to visualise. The majority of Early Pregnancy Assessment Units do not accept referrals for patients who are under 6 weeks pregnant in order to avoid this situation, which not only means a scan appointment is unhelpful, but can also exacerbate anxiety in patients by receiving an inconclusive diagnosis. There has been an increase in PUL patients in recent years due to women taking pregnancy tests earlier and earlier. Patients can then understandably want to be referred if they have spotting or bleeding in the first few weeks of pregnancy and may struggle to wait for an appointment when they are worried, however it is important to remember that while some women may get a positive test at 4 weeks pregnant, at this stage the embryo is barely the size of a pin head. Ultrasound Practitioners will usually ask to scan early pregnancy patients trans vaginally (a small probe is inserted into the vagina) because this means they can get much closer to a very tiny pregnancy sac and hopefully obtain clearer views. When the sac is very tiny there are too many layers to obtain clear pictures through the abdomen. There is no evidence to suggest that internal scans harm the pregnancy in any way and most EPAU clinics will expect to scan vaginally.

What happens if I have a pregnancy of unknown location?

If your pregnancy is not visible on ultrasound, the clinic will usually take some blood tests looking at your HCG levels (Human Chorionic Gonadotrophin). This is a pregnancy related hormone. The presence of this hormone is also what results in a positive urine pregnancy test. You will have this blood test taken and results will usually be back by the next day, then it is likely that you will ask to have the blood test repeated after 48 hours to see if the pregnancy hormone has risen. This will help your clinic find out what is happening with your pregnancy.  There are 3 possible outcomes of a PUL.

  1. Viable pregnancy

If your HCG levels rise well over the 48 hours (ideally they should more or less double within this period) and that indicates that it is likely (but not definitely) that this is an ongoing viable pregnancy which is continuing to grow. You will then probably be asked to return for a further ultrasound after another week or two when the embryo will be considerably larger and should be visible on ultrasound. Most UK clinics work to guidelines that an increase of over 63% will trigger a repeat ultrasound at a later date. 

  1. Failing pregnancy/miscarriage

If your HCG levels drop over the 48 hours then sadly it is extremely unlikely that this pregnancy is continuing to develop. You may or may not have experienced some bleeding or spotting by this time. Depending on the percentage drop of HCG, your clinician will arrange follow up, which may be a further blood test to monitor HCG levels again, or if it has already dropped significantly, they may simply recommend you take a urine pregnancy test again after a couple of weeks to confirm if your hormone levels are now negative and the pregnancy has gone. 

  1. Ectopic pregnancy

Sometimes a pregnancy can grow in the wrong place rather than safely within the uterus. The majority of ectopic pregnancies grow within the fallopian tubes.  Unfortunately this means that the pregnancy almost always cannot safely continue. Clinicians are wary of ectopic pregnancies when HCG levels remain static and neither rise nor fall significantly, especially if a patient is symptomatic in terms of ongoing pain on one side and brown spotting. If your HCG levels are relatively static then your results will usually be reviewed by an on call doctor and you will either have to return again for further HCG blood tests to see if this resolves naturally, or called in to the hospital to discuss possible treatments. Please be reassured that ectopic pregnancy is relatively unusual and far more PUL patients are either too early to see a pregnancy, or the pregnancy has failed but they are not at imminent risk.

See here for more details on ectopic pregnancy and how it is treated.

What is a normal HCG level in a pregnancy of unknown location?

Patients often want to know if their first HCG blood test is “normal” and this is a difficult question to answer as levels can vary hugely in the first few weeks of pregnancy; for example at 5 weeks pregnant they can be anything from 18 to over 7,000 and every woman is different, so one isolated HCG reading is not helpful, clinicians need to see a trend from at least two tests.

What is a persistent PUL?

If your first two HCG blood tests are still inconclusive, and a third blood test still shows no significant drop in the level, then clinicians will call this a “persistent PUL” which is not resolving quickly as the majority do. They will want to keep a close eye on your symptoms (there is no need to be alarmed, they are simply erring on the side of caution because they have not yet fully ruled out the possibility of an ectopic pregnancy). If you have no symptoms and your HCG is considered low, and are clinically well, they may just continue to monitor your bloods, however if the levels still do not drop, or if you develop symptoms such as pain on one side they may want to treat the pregnancy with a medication called methotrexate as they would an ectopic pregnancy. See below for details of NICE guidelines which recommend that clinical symptoms are more significant in this scenario than HCG levels. Please speak to your clinician if you have any concerns or change in symptoms.

 

NB HCG levels vary hugely between patients so it is difficult to read what is a “normal” level

One of the most difficult things for PUL patients is waiting. Usually they will have been referred to an early pregnancy clinic because they have concerns, often due to bleeding or pain, and it is a very worrying time. Due to the nature of the PUL diagnosis there is a lot of uncertainty as you cannot speed up nature. It can be very frustrating not knowing what is happening with a much wanted pregnancy, and very difficult to accept that there is nothing your clinic can do to speed up nature. It is simply a case of waiting to see if your HCG levels rise, and to see if the pregnancy continues to grow.

 

For more information about a diagnosis of Pregnancy of Unknown Location see:

 

https://www.bradfordhospitals.nhs.uk/wp-content/uploads/2020/11/20092316-pregnancy-of-unknow-location-for-web.pdf

https://www.liverpoolwomens.nhs.uk/media/3100/pregnancy-of-unknown-location-pul-gyn_2018-126.pdf

https://nhslguidelines.scot.nhs.uk/media/2233/management-of-ectopic-pregnancy-and-pregnancy-of-unknown-location-july-2022.pdf

https://www.nice.org.uk/guidance/ng126/chapter/recommendations#human-chorionic-gonadotrophin-measurements-in-women-with-pregnancy-of-unknown-location