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Ultrasound Scans During Pregnancy

You're probably excited about your first scan because it gives you a first glimpse of your baby. The person doing the scan (the sonographer) may give you a printout of the image of your baby as a keepsake, however, you will need to ask at the start of your scan.

What is an ultrasound scan?
Ultrasound scans send high-frequency soundwaves through your uterus (womb). The soundwaves bounce off your baby as echoes. These echoes are turned into an image on a screen that shows your baby's position and movements.

Hard tissues, such as bone, reflect the biggest echoes. These appear white in the image, and soft tissues appear grey. Fluids, such as the amniotic fluid that your baby lies in, appear black, because the echoes go through them.

Is ultrasound safe?
Ultrasound scans have been used in pregnancy for decades, and nobody has ever found them to be harmful. Even so, most experts agree that scans shouldn't be done without clear medical reasons.

What is an ultrasound scan used for?
Depending on your stage of pregnancy, scans can:

  • Check that your baby has a heartbeat.
  • Say whether you are pregnant with one baby or twins or more.
  • Detect an ectopic pregnancy, where the embryo implants outside the uterus, usually in the fallopian tube.
  • Find out the cause of any bleeding you may be having.
  • Accurately date your pregnancy by measuring your baby.
  • Assess your baby's risk of Down's syndrome by measuring fluid at the back of your baby's neck at 11 weeks to 13 weeks plus six days (nuchal translucency (NT) scan).
  • Find out why a blood screening test was abnormal.
  • Help with diagnostic tests by showing the position of the baby and placenta.
  • Examine your baby to see if all her organs are normal.
  • Diagnose certain abnormalities, such as spina bifida.
  • Assess the amount of amniotic fluid you have and find out where the placenta lies.
  • Examine the bloodstream in the umbilical cord to see it is functioning well enough to transport sufficient oxygen and nutrition to the foetus.
  • Measure your baby's rate of growth over several scans.

A scan may show if you are expecting a girl or a boy. But if your baby is lying in an awkward position, it's not always easy to tell.

How is an ultrasound carried out?
If you're having a scan in early pregnancy, you'll need to drink a few glasses of water beforehand. Your bladder will then push your uterus out of your pelvis, giving the sonographer a good view of your baby. She will put some gel on your tummy and move a hand-held device (transducer) over your skin to pick up images of your baby.

If your baby is still too deep in your pelvis, or if you are overweight, the images will not be very clear, so a vaginal scan may be necessary. Vaginal scans give a much clearer picture of your baby, especially if you're at an early stage of pregnancy.  Even embryos that are only a few millimetres long will be visible on the TV monitor.

The vaginal transducer is long and narrow to fit comfortably inside your vagina. The sonographer will use a cover similar to a condom and will lubricate this with plenty of gel, so it slides in easily. She won't need to go in very deeply, and it will not harm you or your baby in any way.

Does an ultrasound hurt?
An abdominal scan is painless except for the mild discomfort of the transducer pressing on your tummy if you have a very full bladder. If you are in pain, tell the sonographer. She may ask you to half empty your bladder, which will make the examination more comfortable. You won't usually be asked to fill your bladder for scans in later pregnancy, but check with your doctor first.

Some women prefer a vaginal scan, as it is best done with an empty bladder. You may feel a bit embarrassed, but remember the sonographer does these scans every day. She'll cover you with a sheet, and if you relax your muscles to allow the transducer to slide in easily, it shouldn't be uncomfortable.

When are scans usually carried out?
During your first trimester you may have an early scan at about six weeks or seven weeks. But this will only be if you are experiencing problems, such as pain or vaginal bleeding.

Your first scan is likely to be a dating scan when you are between 10 weeks and 13 weeks plus six days pregnant. This will confirm your due date.

The dating scan is important if you are having screening tests for Down's syndrome, as a correct due date is needed to make the result accurate. You can have a nuchal translucency (NT) scan at 11 weeks and 13 weeks plus six days of your pregnancy, or when your baby measures between 45mm and 84mm. This will, in most cases, be combined with a blood test for increased accuracy.

In your second trimester you should have an anomaly scan at about 20 weeks. This is to check that your baby is developing normally.

In your third trimester, you may be recommended to have a growth scan between 28 weeks and 40 weeks. This will be if you:

  • previously gave birth to a small baby
  • are having twins
  • have other complications, such as diabetes
  • are pregnant with a baby who measures smaller than expected

Do I have to have an ultrasound?
Most women have at least one scan during pregnancy, but you don't have to have one. Scans can give useful information about your pregnancy, and most women find them reassuring. However, many abnormalities can't be seen on a scan, and sometimes the scan findings can cause mums to worry.

What if the scan shows a problem?
You will naturally worry if your scan suggests that there is a problem with your baby. Sometimes a clear diagnosis, such as for spina bifida, can be made from the scan. Or the scan may show minor changes (markers) which are usually nothing to worry about. Occasionally, though, these can be a sign of something more serious, such as Down's syndrome.

If a scan reveals a serious problem, you should be given plenty of support to guide you through all the options. Although such serious problems are rare, some families are faced with the most difficult decision of all: whether to end the pregnancy.

Other problems may mean a baby needs surgery after birth or while in the uterus. Or you may need to prepare for the possibility of your baby needing special care when she's born.

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