When you’re having a baby, one of the standard tests is a pregnancy ultrasound, also known as a pregnancy sonogram. It's called an ultrasound because it works by emitting high-frequency sound waves (which we can't hear) to create an image on a screen. The waves are transmitted and received via a transducer that is placed on your stomach or via a vaginal probe. The sound waves bounce off the part of your body being scanned to form the image.

Why Use Ultrasounds?
Pregnancy ultrasound is used for a variety of reasons. Sometimes this test is used to confirm that you are pregnant and to locate the pregnancy. This can be an early way to detect an ectopic pregnancy. It is also a useful way of finding out whether you are carrying more than one baby. You can also study the placenta to see that it is providing adequate nutrition for the baby. Ultrasound is also useful for monitoring your baby's health and can be used to check on the baby's gestational age, growth, breathing, heart rate and movement. All of this helps the obstetrician to determine whether the baby's development is following normal patterns.

A pregnancy ultrasound is also a key tool for detecting fetal abnormalities, either on its own or in conjunction with other tests. For example, the nuchal translucency scan is an ultrasound test that checks for the likelihood of Down Syndrome. If you need to have other prenatal tests, ultrasound can be used to help obstetricians place the needle for taking a sample of the placenta or the amniotic fluid. Ultrasound may also be used to investigate any unusual symptoms you have during pregnancy, such as vaginal bleeding.

Types of Ultrasound
Depending on the ultrasound technology being used you may get a two-dimensional, three-dimensional or four-dimensional image of your baby. A standard pregnancy ultrasound takes around 20 minutes and will produce a two-dimensional image. If there seems to be a problem, then you may have an advanced ultrasound, which may take half an hour or more. For tests done in early pregnancy, such as those looking for ectopic pregnancies, you may have a transvaginal ultrasound. Three-dimensional ultrasound tends to be used for further evaluation of images created by advanced ultrasound tests. If your baby seems to be growing slowly or you have circulation problems, Doppler imaging can be used to find out more. Fetal echocardiography is a type of ultrasound used to check your baby's heart for abnormalities.

Getting a Scan
Scans may take place at different times, depending on the reason for the scan. You may have a scan around seven weeks to confirm the pregnancy and the gestational development of the baby. A scan for Down Syndrome may take place between 11 and 14 weeks. Another scan may take place between 18 and 20 weeks to check on the weight, growth and position of the baby. As a bonus, you can also find out the sex of your child from a pregnancy ultrasound done at this time. Other scans may take place as required if there are any risks in the pregnancy.

Ultrasounds are conducted by sonographers or radiographers. Sometimes you are asked to drink water before going for a scan to help doctors to see the baby better. You lie on a table and the doctor puts a small amount of clear gel onto your abdomen. The doctor then places the transducer on your abdomen and moves it around. The sound waves received will create a black-and-white picture that will appear on the screen in the room. You may also receive a printout of this picture. Sometimes you can see the baby clearly; at other times the picture may be distorted. This depends on when the scan is done and the position of the baby. In later scans, it's easier to identify limbs and features. You will usually get the results of the pregnancy scan immediately.

Next Steps
Pregnancy ultrasound can detect fetal death, genetic abnormalities, congenital malformations, problems with the amniotic fluid and placenta, ovarian, pelvic and uterine abnormalities and tumors. In most cases, a pregnancy ultrasound confirms that your baby is developing normally. If there is any cause for concern, you may have additional ultrasound tests or be recommended for other tests. Pregnancy ultrasound is usually a non-invasive technique that is completely safe. It has been in use for more than 40 years and it does not use radiation.