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Pregnancy ultrasound (antenatal ultrasound)

An antenatal ultrasound scan during pregnancy is the first time parents-to-be get to see a baby moving in the womb.

High-frequency sound waves, inaudible to the human ear, are transmitted through the abdomen through a device called a transducer to look at the inside of the abdomen. With antenatal ultrasound, the echoes are recorded and transformed into video or photographic images of your baby.

The scan can be used during pregnancy to show images of the baby, amniotic sac, placenta and ovaries. Major anatomical abnormalities or birth defects can show up on an ultrasound.

Most antenatal ultrasound procedures are performed on the surface of the skin, using a gel to help improve the image quality.

A transvaginal ultrasound is an alternative procedure performed using a tubular probe that is inserted into the vaginal canal. This method of ultrasound, which produces an image quality that is greatly enhanced, is not a common antenatal procedure. However, it may be used early in pregnancy to get a clearer view of the uterus or ovaries if a problem is suspected. It may also be used early in pregnancy to determine how far along you are in your pregnancy (gestational age).

Is antenatal ultrasound safe?

Studies have shown ultrasound is not hazardous. There are no harmful side effects to you or your baby. In addition, the scan does not use radiation, as X-ray tests do.

When is an ultrasound performed during pregnancy?

A scan at around 12 weeks gestation is offered as standard in the NHS, known as a ‘dating scan’. It will give an accurate due date and check several important details:

  • The age of your baby
  • Whether there is more than one baby
  • The baby’s heartbeat
  • Whether there are any obvious abnormalities
  • Whether your ovaries are in a healthy condition.

A second scan is generally performed for all pregnant women at around 18-21 weeks gestation (the mid-pregnancy ultrasound scan). During this scan, the doctor will confirm that the placenta is healthy and attached normally and that your baby is growing properly in the uterus. It is called the anomaly scan as it checks for any structural abnormalities a baby has. The baby's heartbeat and movement of its body, arms and legs can also be seen on the ultrasound.

If you wish to know the gender of your baby, it can usually be determined at 20 weeks. Be sure to tell the person performing the scan whether or not you want to know the gender of your baby (some hospitals have a policy of not revealing the gender). Please note that ultrasound is not a foolproof method to determine your baby's gender; there is a chance that the ultrasound images can be misinterpreted.

Later in pregnancy, scans may be used if you have had complications in previous pregnancies or have a medical condition, such as diabetes or high blood pressure or to determine the:

  • Health of the baby
  • Placenta location
  • Amount of amniotic fluid around the baby
  • Position of the baby
  • Baby's expected weight.
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