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Ultrasound in pregnancy
Published by Bupa's health information team, February 2010.
This factsheet is for women who are having an ultrasound scan during pregnancy, or who would like information about the procedure.
Ultrasound is used to monitor your baby's growth and check for physical abnormalities. It uses high-frequency sound waves and their echoes to create moving three-dimensional (3D) or four-dimensional (4D) images of your growing baby. The pictures (scans) are black, white and grey and are displayed on a screen.
You will meet the obstetrician or sonographer carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.
About ultrasound in pregnancy
Ultrasound scans in pregnancy are usually performed by an obstetrician or sonographer. Obstetricians are doctors specially trained in pregnancy and childbirth. Sonographers are technicians specially trained in taking ultrasound scans.
There are different reasons for doing ultrasound scans at different stages during pregnancy. All pregnant women have two routine scans: a dating scan, and a scan to check that the baby is developing normally (fetal anomaly scan). Other scans are offered to certain pregnant women because of their age and medical or family history.
You will normally have an ultrasound scan between 10 and 14 weeks of pregnancy to check when your baby is due. This is often known as the '12-week scan'. Knowing the baby's gestational age can help monitor important milestones during your pregnancy. This scan will also tell you if you're expecting more than one baby.
If this scan is done between 11 and 14 weeks of pregnancy, it can also help to estimate the chance that your baby has Down's syndrome.
Fetal anomaly scan
You will have another scan to check your baby's development. This is commonly known as the '20-week scan', though it can be between 18 and 22 weeks of pregnancy. During this scan, your obstetrician or sonogrpaher will check for abnormalities that can be seen with a scan. He or she will check your baby's heart, brain, kidneys, liver and spine, and measure the arms, legs and head.
At this scan, your sonographer will also check the position of the placenta, which provides vital nutrients and oxygen-rich blood to your baby. If the placenta is lying unusually low in the womb, this is called placenta praevia. This usually resolves before the baby is born, but if it doesn't, you may need to have caesarean delivery (an operation to deliver your baby through your tummy).
Other ultrasound scans in pregnancy
Ultrasound is used during procedures to collect amniotic fluid (amniocentesis) or tissue samples from the placenta (chorionic villus sampling). The amniotic fluid and placenta contain your baby's DNA and can accurately confirm if your baby has a genetic disorder.
You may have other scans during pregnancy if your routine scans or antenatal appointments suggest there may be a problem with your baby or the placenta. For example, you might have more ultrasound scans if:
- your 20-week scan showed a low-lying placenta
- you have diabetes and are at risk of having a large-for-gestational-age baby
- your midwife thinks your baby may be breech (bottom-down rather than head-down)
- your baby is smaller than it should be for your stage of pregnancy
- you have vaginal bleeding during pregnancy
One type of ultrasound scan that is sometimes used is called Doppler ultrasound. This monitors flow in blood vessels and can be used to check placenta function. Problems with the placenta can affect your baby's growth and development. Doppler scans are only done if your obstetrician or midwife think there might be a problem with the placenta.
Fetal echocardiogram is a type of Doppler ultrasound done by a specialist to examine your baby's heart before birth. It's usually done at around 18-24 weeks by scanning through the abdomen. It can also be done earlier in pregnancy through the vagina. Fetal echocardiogram is only performed if a routine scan shows abnormalities, or if your baby is at risk of having heart problems.
A person having an ultrasound scan
Preparing for your ultrasound
Ultrasound scans in pregnancy are usually arranged by your GP or midwife. You usually have the scan in an out-patient department in hospital.
Please read your appointment letter for instructions on how to prepare for your scan. In early pregnancy you may need to have a full bladder, so you will need to drink fluids about an hour before the scan. A full bladder helps to lift the large bowel out of the pelvis so that the womb can be seen more easily.
Usually only one person is allowed to accompany you into the ultrasound room.
What happens during an ultrasound scan
An ultrasound scan usually takes five to 20 minutes to perform. A Doppler scan or fetal echocardiogram may take longer depending on the investigation.
The ultrasound scanner looks a bit like a home computer system. There is a hard-drive, keyboard and a display screen. There is a sensor that your sonographer holds. The sensor sends out sound waves and picks up the returning echoes. Pictures of the baby are displayed on the screen. These pictures are constantly updated, so the scan can show your baby's movements.
You may have the ultrasound scan through the vagina or abdomen depending on how many weeks pregnant you are. Both the routine dating scan and the fetal anomaly scan are usually abdominal scans.
This method is used if the scan is being done in early pregnancy (before about 12 weeks) when the embryo is very small. A vaginal scan gives a better view compared to an abdominal scan.
You will be asked to lie on your back and a lubricated sensor (the size of a tampon) is gently inserted into your vagina. The sensor is usually covered with a condom. Please tell your examiner if you suffer from a latex allergy, so that a suitable condom can be used.
This method is usually used for scans after about 12 weeks of pregnancy.
You will be asked to lie down on your back. Your sonographer or obstetrician rubs clear gel onto your skin on your lower abdomen. The gel allows the sensor to slide easily over your skin and helps to produce clearer pictures. The sensor is held firmly against your skin and moved over the surface. If you look at the screen, you'll see a picture of your baby.
You can go home when the scan is finished. Permanent copies of the scan are stored on computer, saved on disc or printed.
Your sonogrpaher may give you a printed copy of the scan to take home with you after having your routine scans. Some hospitals save the scans on a DVD for you to take home. You may need to pay for the picture or DVD.
Your sonographer or obstetrician will usually explain the details of your ultrasound scan to you during or straight after the scan.
What are the risks?
Ultrasound examination is painless and safe. It does not use radiation and so carries none of the associated risks. Ultrasound is not known to have any harmful effects, and is not known to harm your baby. It is considered safe to use during pregnancy.
- National Childbirth Trust (NCT)
0870 990 8040
- Emma's diary
Emma's Diary® is published on behalf of the Royal College of General Practitioners.
- Information for patients having an ultrasound. Royal College of Radiologists, 2008. www.rcr.ac.uk
Antenatal care: Routine care for the healthy pregnant woman. National Institute for Health and Clinical Excellence (NICE), 2008. www.nice.org.uk
- Your second trimester: Your '20 week' scan. Emma's Diary, Royal College of General Practitioners. www.emmasdiary.co.uk, accessed 30 September 2009
- Amniocentesis and chorionic villus sampling. Royal College of Obstetricians and Gynaecologists, 2005. www.rcog.org.uk
- The investigation and management of the small-for-gestational-age fetus. Royal College of Obstetricians and Gynaecologists, 2002. www.rcog.org.uk
- Vaginal bleeding in pregnancy. National Library of Medicine. www.nlm.nih.gov, accessed 30 September 2009
- Fetal echocardiography. National Library of Medicine. www.nlm.nih.gov, accessed 30 September 2009
- Ultrasound imaging of the pelvis. Radiololgy Society of North America. www.radiologyinfo.org, accessed 20 September 2009
- Your first trimester: dating scan. Emma's Diary, Royal College of General Practitioners. www.emmasdiary.co.uk, accessed 30 September 2009
This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.
Publication date: February 2010.