Written by Dr Sarah Merritt

Pregnancy of unknown location can be a daunting term, which may bring uncertainty, anxiety and questions of  ‘Am I pregnant?’, ‘Why can’t my baby be seen?’

A pregnancy of unknown location means that a pregnancy cannot be seen, either inside or outside the womb on a transvaginal (internal) ultrasound scan, even though the urinary pregnancy test is positive.

The main reasons as to why a pregnancy of unknown location has occurred are:

  • The pregnancy may be a normal developing pregnancy, which is too small to be seen on a transvaginal scan

A pregnancy test will become positive about a week or two before a normally developing pregnancy in the womb can be seen on scan.  This is the most likely final outcome if there have been no symptoms such has bleeding vaginally or pain, uncertainty of the last period date or if a woman has a longer menstrual cycle.  A small pregnancy sac in which the baby will eventually normally grow can be seen at about 4 weeks and 3 days gestation in a woman with a 28 day cycle.  A baby is not seen until between 5 and a half to 6 weeks gestation in a healthy ongoing pregnancy.

  • The pregnancy may miscarry from within the womb

A pregnancy that is sadly going to fail does not grow at a normal rate and may not be seen on scan initially.  There is no specific time that the pregnancy will be seen on scan before it miscarries. Sometimes the pregnancy may never be seen at all before it fails.

  • An ectopic pregnancy, where the pregnancy grows most commonly outside of the womb, often in the fallopian tube or in the wrong place in the womb such as the cervix or within a previous caesarean section scar

An ectopic pregnancy may be too small to be seen on an initial scan.  There is no set time or level of pregnancy hormone that indicates when an ectopic will be seen on scan.  Sometimes it will fail and never be seen.

  • A miscarriage has already occurred

If period like or heavier bleeding has occurred the pregnancy may have already passed from the womb and will not be seen as the womb is now empty.  The pregnancy test is still positive as the pregnancy hormone level takes time (sometimes several days) to drop.

If a PUL is the outcome of the scan then women are followed up in an Early Pregnancy Unit.  A blood test is taken to measure the main pregnancy hormone released by a pregnancy; hCG (human chorionic gonadotrophin) and progesterone, a hormone which usually is found in a higher levels in a healthy on-going pregnancy. Depending on the test results and how well a woman is will help determine if and when further scans and/or blood tests are required.

The hormone tests themselves do not confirm where the pregnancy is located.  The amount of hCG is related to the size of the pregnancy tissue, either within or previously within the body (in women who have already miscarried) and progesterone indicates the speed at which the pregnancy is growing.  Progesterone helps support a pregnancy.

Typically a high progesterone test and low hCG levels probably indicate an early healthy pregnancy within the womb and often a second trans vaginal scan will be arranged when it is predicted the hCG level will be above a level of 1000.  The hCG level roughly doubles every 48 hours in a normal pregnancy growing inside the womb.

If the progesterone level is in-between being very low or very high i.e mid range, there is more of a chance that the pregnancy will either result in a miscarriage or ectopic pregnancy.  Usually the hCG level will be repeated in 48 hours to see the trend.  If the hCG has increased usually another scan will be performed to try to locate the pregnancy, if it’s the same or reducing then the pregnancy, wherever it is located is probably failing.  Repeat hCGs will be taken until the level is under 20-25.  Typically in an ectopic pregnancy or a miscarriage the hCG level will not increase by as much as a healthy ongoing pregnancy within the womb.

If the progesterone is very low then it is most likely that the pregnancy is not continuing to grow and develop and is either failing or will fail regardless of where it is.  Depending on what the starting hormone levels are, will determine whether and when further hormone levels are taken or if a pregnancy test is advised one to two weeks later.  Vaginal bleeding is common and usually resolves within 2-3 weeks.  Occasionally this can be very heavy or on going and the Early Pregnancy Unit would advise a woman to attend the Early Pregnancy Unit or the Emergency Department if the bleeding is excessive.

There will be some pregnancies which will grow normally in the womb with lower than expected progesterone levels and there will be some ectopic pregnancies where the hCG level increases as a normally growing pregnancy does. Until either the pregnancy is located or the hCG has fallen to non pregnant levels then any worrying symptoms such as severe pain may indicate an ectopic pregnancy.  Ectopic pregnancies can cause internal bleeding and any woman with a PUL will be advised by their Early Pregnancy Unit to attend hospital immediately if they have severe or ongoing pain on order to determine whether an ectopic is present or not.


If the pregnancy does result in an ectopic pregnancy or miscarriage, Early Pregnancy Units will be able to help regarding physical and psychological support and provide information on support groups.  It is important that any pregnancy loss is recognised and time given to grieve regardless of how early in the pregnancy the loss occurred at.  All women and partners should be able to access support and guidance if they want to. Losing a baby is a personal experience that affects people differently.

For further support and information please see the ectopic pregnancy trust, the miscarriage association website or Royal College of Obstetricians and Gynaecologists websites – links below:





Dr Sarah Merritt

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