What is an ultrasound scan?
An ultrasound picture is formed using sound waves, which are passed through the uterus and reflected back as an image on a screen.
Ultrasound scans in pregnancy may be routine or they may be offered because of pain or bleeding or because of problems in a previous pregnancy.
How is it done?
There are two ways of doing an ultrasound scan.
In early pregnancy, especially before 11 weeks, it is usual to have a trans-vaginal (internal) scan, where a probe is placed in the vagina. This gives the clearest and most accurate picture in early pregnancy. It may also be offered after 11 or 12 weeks if a trans-abdominal scan doesn’t give a clear enough picture.
From 11 or 12 weeks, including at the routine booking-in scan, it is more common to have a trans-abdominal scan. The person doing the scan spreads a special gel on your lower abdomen (below your belly button and above the line of pubic hair). He or she then moves the scanner over the gel, sometimes pressing down, until the uterus (womb) and pregnancy can be seen.
What if I don’t want an internal scan?
If you don’t want a trans-vaginal scan, you can ask for a trans-abdominal scan. That may give some information about your pregnancy, but it is less clear than an internal scan and that could possibly delay diagnosis.
Can scans harm the baby?
There is no evidence that having a vaginal or an abdominal scan will cause a miscarriage or harm your baby. If you bleed after a vaginal scan, it will most likely be because there was already blood pooled higher in the vagina and the probe dislodged it.
When can I have a scan? When can you see the baby’s heartbeat?
An ultrasound scan may be able to detect a pregnancy and a heartbeat in a normal pregnancy at around 6 weeks, but this varies a great deal and isn’t usually advised. All too often, a scan at 6 weeks shows very little or nothing, even in a perfectly developing pregnancy, whereas waiting a week or 10 days will make the findings much clearer. Read more about early scans.
Most pregnant women are referred for their first routine ultrasound scan somewhere between 11 and 18 weeks of pregnancy. The purpose of the scan is:
- to confirm that there is a heartbeat
- to assess the baby’s size and growth
- to estimate the delivery date and
- to check whether there is one baby, or twins or more.
Some women may be offered a nuchal scan between 11 and 14 weeks. The purpose of this scan is to try to detect some chromosome abnormalities, such as Downs syndrome.
Many hospitals also offer a further anomaly scan at 20 weeks, making a more detailed check of the baby’s development.
You can find out more about nuchal and anomaly scans at the website of the charity ARC – Antenatal Results and Choices
Sadly, sometimes these scans show that the baby has died, possibly some weeks earlier and often without any signs or symptoms such as bleeding or pain. This is often called a “missed” or “delayed” miscarriage. This can come as a considerable shock and it may take time before you can take this information in.
You may also have to make some difficult decisions about how to manage the miscarriage process. You can read more about this here.
You may be referred for an early scan because of vaginal bleeding or spotting, or possibly because you have had problems in a previous pregnancy.
The best time to have a scan is from about 7 weeks’ gestation when it should be possible to see the baby’s heartbeat in a normal pregnancy. But it can be hard to detect a heartbeat in early pregnancy and in those cases it can be hard to know whether the baby has died or not developed at all, or whether it is simply smaller than expected but still developing.
For that reason, you may be asked to return for another scan a week or so later. At that time, the person doing the scan will be looking for a clear difference in the size of the pregnancy sac and for a developing baby and a heartbeat.
Sometimes, it can take several scans before you know for sure what is happening. It can be very stressful dealing with this uncertainty – some women describe it as being “in limbo”. You may need to find some support for yourself if this happens to you.
There’s a heartbeat, but I’m still bleeding…
If the scan does pick up a heartbeat and the baby appears to be the right size according to your dates, this can be very reassuring, even if you are still bleeding.
Research has shown that if you see a heartbeat at 6 weeks of pregnancy, the chances of the pregnancy continuing are 78%.
A heartbeat at 8 weeks increases the chance of a continuing pregnancy to 98% and at 10 weeks that goes up to 99.4%.
So things could still go wrong and sadly sometimes do, but as long as there is a heartbeat, the risk of miscarriage decreases as the weeks go by.
In some cases, if there is no sign of a pregnancy in the uterus, you may be given a blood test and possibly asked to return two days later for a repeat test.
These blood tests measure the level of the pregnancy hormone ßhCG. In a normally developing pregnancy the hormone levels double about every 48 hours and if the pattern is different, this can help to identify what is happening to the pregnancy.
If there is no sign of a pregnancy in the uterus and you have symptoms that suggest ectopic pregnancy, you are more likely to have both a blood test and an investigation called a laparoscopy, which is done under general anaesthetic. You can read more about this in our leaflet Ectopic pregnancy.
Scan results – and what they mean
The ultrasound scan may show:
- A viable ongoing pregnancy. There is a heartbeat (or heartbeats if it’s a twin or multiple pregnancy) and the pregnancy is the “right size for dates” – that is, the size that would be expected based on the first day of your last period. Those are positive signs, but if you continue to bleed, you may need a further scan in a week or two to check what’s happening.
- An ongoing pregnancy that suggests a problem. Perhaps the pregnancy is much smaller than it should be according to dates or the heartbeat is particularly slow or faint. Perhaps there is something that suggests a problem with the baby’s development. With a twin or multiple pregnancy, the scan may show that one (or more) baby has a heartbeat and one (or more) doesn’t. You may be asked to come back for another scan, possibly in a week or two when things should be clearer.
- A pregnancy of unknown location (PUL). The pregnancy is too small for the heartbeat to be visible, or there may be nothing much to see at all and it’s not clear what is happening. You will probably be asked to come back for another scan, possibly in a week or two when things should be clearer. Or if the doctor thinks you might have an ectopic pregnancy, you will have blood tests and/or a laparoscopy.
- A complete miscarriage. The pregnancy has miscarried. There may still be a small amount of tissue or blood in the uterus.
- A non-viable pregnancy. This means a pregnancy that hasn’t survived but hasn’t yet miscarried. You may hear this described in one of the following ways:
- Missed miscarriage (also called silent or delayed miscarriage or early embryonic demise) This is where the baby has died or failed to develop but your body has not miscarried him or her. The scan picture shows a pregnancy sac with a baby (or fetus or embryo) inside, but there is no heartbeat and the pregnancy looks smaller than it should be at this stage. You may have had little or no sign that anything was wrong and you may still feel pregnant.
- Blighted ovum or anembryonic pregnancy (which means a pregnancy without an embryo). This is a rather old-fashioned way of describing a missed miscarriage (see above). The scan picture usually shows an empty pregnancy sac.
- Incomplete miscarriage The process of miscarriage has started but there is still pregnancy tissue in the uterus (womb) and you may still have pain and heavy bleeding.
In all of these situations, the pregnancy will fully miscarry with time, but there are several ways of managing the process. You may be offered a choice, or the hospital might make a recommendation. In most cases, you should be able to have time to think about what you can best cope with. You can read more here.
The ultrasound scan might show
- An ectopic pregnancy. This means a pregnancy that is developing outside the uterus (Ectopic means “out of place”). Ectopic pregnancies usually develop in one of the Fallopian tubes, but they can develop elsewhere inside the abdomen. You can read more in our leaflet Ectopic pregnancy.
- A molar pregnancy. This is a pregnancy where the baby can’t develop but the cells of the placenta grow very quickly. It can’t always be diagnosed on scan so you might find out only after the miscarriage. You can read more in our leaflet Hydatidiform Mole.