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Ultrasound in pregnancy

This factsheet is for women who are having an ultrasound scan during pregnancy, or who would like information about the procedure.

Ultrasound can be 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. Details of the procedure may also vary from country to country.

Click on the tabs below for more information about ultrasound.

Published by Bupa's health information team, March 2010.

About

About

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. In some countries, women are offered scans early in pregnancy to confirm the pregnancy and check when their baby will be due; and later in pregnancy to check that the baby is developing normally. Scans may also be offered to certain pregnant women because of their age and medical or family history.

First trimester

You may be offered an ultrasound scan in the first 12 weeks of your pregnancy to confirm the pregnancy, check for a heartbeat and check when your baby is due. Knowing how many weeks old your developing baby is (the gestational age) can help doctors monitor important milestones during your pregnancy. A scan done at this time can also tell you if you're expecting more than one baby, and may be able to help to estimate the chance that your baby has Down's syndrome.

Second trimester

You may be offered another scan to check your baby's development later on in your pregnancy. At this stage, your obstetrician or sonographer can check for abnormalities that can be seen with a scan. He or she may check your baby's heart, brain, kidneys, liver and spine, and measure the arms, legs and head.

Your sonographer will also be able to 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 often resolves before the baby is born, but if it doesn't, you may need to have a caesarean delivery (an operation to deliver your baby through your abdomen).

Other ultrasound scans in pregnancy

You may be offered more scans during pregnancy if your doctor or midwife thinks there may be a problem with your baby or the placenta. For example, if:

  • a previous scan showed a low-lying placenta
  • you have diabetes and are at risk of having a large baby
  • your midwife thinks your baby may be in a breech position (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
Ultrasound is also 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.

Doppler ultrasound

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 thinks there might be a problem with the placenta.

Fetal echocardiogram

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 your abdomen (tummy). It can also be done earlier in pregnancy through your vagina. You may be offered a fetal echocardiogram if a previous scan has shown abnormalities, or if your baby is at risk of having heart problems.

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 for you or your baby. It is considered safe to use during pregnancy.

Having an ultrasound

Having an ultrasound

Preparing for your ultrasound


Ultrasound scans in pregnancy are usually arranged by a doctor or midwife and take place in a hospital or clinic.

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.

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 your vagina or abdomen depending on how many weeks pregnant you are.

Vaginal scan


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.

Abdominal scan


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. Your sonographer may give you a printed copy of the scan to take home with you. Some clinics and hospitals save the scans on a DVD for you to take home. You may need to pay for the picture or DVD.

Results


Your sonographer or obstetrician will usually explain the details of your ultrasound scan to you during or straight after the scan.

Sources

Sources

  • Information for patients having an ultrasound. Royal College of Radiologists, 2008. www.rcr.ac.uk
  • Ultrasound: sonogram. American Pregnancy Association. www.americanpregnancy.org, published March 2006
  • 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. This content was compiled by Bupa based on clinical information and practice current as at the stated date of publication. Content is likely to reflect clinical practice in a particular geographical region (as indicated by the sources cited) – accordingly, it may not reflect clinical practice in the reader’s country of habitation. This content is intended for general information only and does not replace the need for personal advice from a qualified health professional. Photos and videos are only for illustrative purposes and do not reflect every presentation of a condition.

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