Pregnant mom Karin Field of Toronto had two questions she hoped an ultrasound would answer. One, would her expected third baby be healthy? And two – since her previous two babies had been born a few weeks early – was her cervix beginning to shorten up too early?

While an ultrasound is an opportunity to get a first look at your baby, it can also answer questions about your expected baby and about the baby’s environment – the location of the placenta, amount of amniotic fluid and condition of the cervix, for example. By measuring the baby’s size, the ultrasound can also be used to give a good estimate of the baby’s age and expected date of birth. It can tell you if there is more than one baby and can detect some problems in the baby’s development and signs of genetic problems. One part of many ultrasounds is the measurement of the nuchal translucency – a fold on the back of the baby’s neck – which may indicate a higher risk that the baby has Down’s syndrome.

Depending on the baby’s position – some modestly keep their legs crossed during the procedure – the ultrasound might reveal the baby’s gender.
If you’re unsure about what happens during an ultrasound, we’ve compiled some basic facts before you head into the examining room.

What is an ultrasound?

The ultrasound machine uses a transmitter (held in the technician’s hand) to send high frequency sound waves into the mother’s uterus. Although they are sound waves, they are so high in frequency that humans can’t hear them. When the waves hit the baby’s bones and other tissues, they are bounced back and picked up again by the transmitter, then translated by the computer into images.

This procedure has been widely used for about 30 years and is considered to be very safe.

When are ultrasounds done? An ultrasound can be done at any stage of pregnancy. One might be recommended early in your pregnancy if you’ve had some bleeding or if the doctor suspects the embryo has implanted in the wrong place (as in an ectopic pregnancy).

Many caregivers routinely recommend an ultrasound at around 18 or 19 weeks to check for Down’s syndrome and other abnormalities, as well as confirming the baby’s due date.

Later in pregnancy, an ultrasound can be done to determine the cause of unexpected bleeding, to find out the baby’s position, to estimate the baby’s size and learn other information. In some cases, such as when the baby’s rate of growth needs to be monitored, a series of repeated ultrasounds may be recommended.