Pregnancy Ultrasound

Definition

A pregnancy ultrasound is an imaging test that uses sound waves to see how a baby is developing in the womb.

Alternative Names

Obstetric ultrasonography.

How the test is performed

Patients lie down for the procedure. The sonographer places a clear, water-based gel on your belly and pelvis area and then moves a hand-held probe over the area. The gel helps the probe transmit sound waves. These waves bounce off the body structures, including the developing baby, to create a picture on the ultrasound machine.

In some cases, a pregnancy ultrasound may be done by placing the probe into the vagina.

How to prepare for the test

A full bladder is necessary to get a good picture. Therefore, you may be asked to drink 2 to 3 glasses of liquid an hour before the test. You should not urinate before the procedure.

How the test will feel

There may be some discomfort from pressure on the full bladder. The conducting gel may feel slightly cold and wet.

Why the test is performed

Some doctors order an ultrasound when they think there may be a problem with the pregnancy or if there is a question about how far along the pregnancy is.

A pregnancy ultrasound may be done in the first trimester to:

• Confirm pregnancy
• Determine the baby’s age
• Look for problems, such as ectopic pregnancies or miscarriage
• Look for multiple pregnancies (twins, triplets, etc.)
• Identify problems of the placenta, uterus, cervix, and ovaries

A pregnancy ultrasound may also be done in the second and third trimesters to:

• Determine the baby’s age, growth, position, and sometimes gender
• Identify any developmental abnormalities
• Look at the placenta, amniotic fluid, and assess fetal well being

We perform a nuchal translucency study at 11-13 weeks of pregnancy to look for signs of Down syndrome or other developmental problems in the developing baby. This test is often combined with blood tests to improve the accuracy of results.

The total number of scans will depend on whether a previous scan or blood test has detected problems that require follow-up testing.

What the risks are

Current ultrasound techniques appear to be safe and there is no documented risk to women or their developing babies. Ultrasound does not involve ionising radiation, such as that used when taking an x-ray.