You can have the 18-22 week ultrasound no matter what prenatal genetic screening choice you make. This ultrasound gives you information about the health of the baby and other aspects of the pregnancy. It is sometimes called the second trimester scan or the detailed anatomy scan.

How to get the ultrasound

This ultrasound is typically done in the second trimester, between 18 and 22 weeks of pregnancy. Talk with your health-care practitioner if you would like to have this ultrasound. In Ontario, this test can be arranged by:

• doctors (such as family doctors, obstetricians)
• nurse practitioners
• midwives

Your health-care practitioner should give you a requisition form, and might schedule this ultrasound for you. Your health-care practitioner might instead ask you to book the ultrasound yourself.

What this ultrasound will look at

Your baby has now grown enough in size to have a detailed look at your baby.  The 18-22 week ultrasound will examine how the baby is growing and developing. This ultrasound can provide lots of information about the pregnancy, including:

• how the baby's internal organs and structures are developing (like the heart, brain, kidneys, spine, arms, and legs)
• whether the baby is the right size for its age
• the position of the baby
• how active the baby is
• the amount of fluid around the baby
• the location of the placenta and the umbilical cord
• your own cervix, uterus, ovaries and bladder
• the sex of the baby, depending on the position of the baby. Checking for the sex of the baby is not one of the goals of this ultrasound. 

How to prepare for your ultrasound

It is important that you ask the clinic if there are any special instructions before your appointment. Every ultrasound clinic has different requirements. Commonly you will be asked to drink 1 Litre of water before the ultrasound to fill your bladder. Filling your bladder makes it easier to take the ultrasound images.

How the ultrasound is done

A doctor or ultrasound technologist puts a warm gel on your abdomen and uses a hand-held scanning device to get ultrasound images. Sometimes, the ultrasound is done through the vagina to get better images of the baby.

The scanning device creates sound waves that the human ear cannot hear. The ultrasound machine picks up the sound waves that bounce off the baby and turns them into an image on a screen. Ultrasound does not use radiation, and is safe in pregnancy.