As part of your antenatal care ultrasound scans will be offered to you at approximately 12 weeks and 20 weeks of pregnancy. Occasionally it is advisable for a woman to have several scans to check on her pregnancy.
What is an ultrasound?
An ultrasound is a black and white image, seen on a TV screen, created by sound waves. It is usually painless and current evidence demonstrates it is harmless to both you and your baby.
Must I have an ultrasound scan?
You do not have to have a scan if you do not wish to. Please discuss with your midwife/GP/Consultant if you require further information or wish to avoid any particular scan. Ultrasound may be offered for different reasons:
Early Pregnancy (12 – 14 weeks)
In early pregnancy it is possible to measure the size of the baby and so calculate the date your baby is due. In most cases this is a more accurate way of estimating the baby’s due date than using period dates. The scan will also tell us that the pregnancy is progressing normally and if you are expecting more than one baby. An early scan is sometimes performed vaginally (internally) especially if very early in pregnancy, however, scans are usually only performed earlier than 12 weeks when there is a clinical indication, for example, if there has been bleeding or concern about an ectopic pregnancy (pregnancy in the fallopian tube).
If you have requested a screening test for Down, Edwards and Patau syndromes a measurement of the back of the baby’s neck (nuchal translucency) will also be done at this scan as part of the Combined Test (nuchal translucency and blood test). Your community midwife will complete a request form at your booking appointment for you to bring with you to your scan. When you have had your scan you will need to go to the nearby phlebotomy clinic to have a blood test. It is important that this is done immediately after the scan. If the baby is not in a good position and it has not been possible to take this measurement then you will be informed you will need a blood test called the Quadruple test. This is usually performed by your community midwife at your 16-week appointment.
Sometimes the screening result for your baby will come back with an increased risk of Down, Edwards or Patau syndrome. If this happens you will get a phone call from a midwife inviting you to come back to the hospital for an appointment with the Fetal Medicine team. You may be offered diagnostic tests such as amniocentesis or CVS if appropriate. Sometimes the Fetal Medicine team may arrange for you to attend another hospital to have further investigations or to speak with specialist teams who may be able to offer further treatment to you and your baby. It is important for you to get as much information as possible. You can also contact the charity Antenatal Results and Choices (ARC). ARC has information about screening tests and how you might feel if you are told your baby does have or might have a problem. The charity has a helpline that can be reached on 0845 077 2290, or 020 7713 7486 from a mobile, Monday to Friday, 10am-5:30pm. The helpline is answered by trained staff, who can offer information and support
Screening for defects in your baby’s anatomy (around 20 weeks)
This mid-pregnancy scan is the best time to take a detailed look at your baby’s anatomy from top to toe in order to check that it is developing normally. If it has not been possible to fully check your baby at this scan you will be offered another appointment around 23 weeks. Most babies are healthy but some have problems that could be serious. It is important to remember that the purpose of the scan is to look for potential problems so it is best not to bring too many people with you into the scan room. If you would not wish to know if your baby has an abnormality it may be best to decide not to have this scan. You can discuss this with your community midwife.
If any abnormality is discovered the significance will be discussed with you at the earliest opportunity by a senior member of the medical staff – usually that day or the day afterward. Where a problem is found or suspected you will be referred to the Fetal Medicine Clinic. This is a team of specialist doctors and midwives who are trained to look at babies in the womb with suspected abnormalities.
Late Pregnancy (24 – 42 weeks)
Some women will be advised to have further ultrasound scans during pregnancy. These can be particularly helpful when there are complications either in this or previous pregnancies. A late scan can help determine the health of the baby by measuring the baby’s growth and the amount of fluid around it. It may also be used to identify the position of the placenta (afterbirth) if there was the possibility of it being low on your mid-pregnancy scan. Women who are expecting more than one baby will be offered regular scans of the babies’ growth throughout the pregnancy as these babies need a closer watch kept on them
Potential problems and difficulties
A full bladder will often help the examination, but the quality of the image obtained will depend on the size of the mother and position of the baby. A full bladder is required for the dating scan and the 20-week scan.
There are limitations to what scans can pick up. Not every abnormality can be seen on the scan. This means that there is a small chance that a baby could be born with an abnormality although the scan appeared normal.
Boy or girl? – It is not hospital policy to routinely determine the sex of the baby. However, if you want to know the sex of the baby you will be given the option of finding out if it is easy to see. The accuracy of telling the sex of the baby, however, cannot be guaranteed. You will need to have decided before your scan if you wish to know the baby’s sex and ask the sonographer before the scan begins. Unfortunately, we are not able to offer you a repeat scan just to find out the sex of the baby if not seen at the time of your routine scan.
When you have your scan an image of your baby can be purchased at a charge of £5 a copy. Ideally, the payment should be made by credit or debit card in the department. Cash payments can be made but not in the same department.