What to expect from your 20-week ultrasound

If you are around 20 weeks pregnant, you’re probably getting ready for your first big ultrasound.

An ultrasound is a non-invasive prenatal test done by a medical professional with a special wand called a transducer. A technician uses the transducer on the exterior of the belly to ensure your baby is developing properly and see how the placenta and umbilical cord are positioned.

But that’s not all that happens! That’s right; at 20 weeks, you are also usually able to learn your baby’s sex. For many, it’s an exciting point in pregnancy.

More: “Creature” pops up in mom’s ultrasound, and he doesn’t look friendly

Here’s what to expect during your 20-week ultrasound.

What does the ultrasound show?

Ultrasound technology has improved a lot since its advent. If Baby cooperates, you can see fingers, toes, spines and even a little face. Also, you may be able to see the baby’s anatomy. Make your intentions known about finding out the sex (whether you want to or don’t), so that the ultrasound tech knows not to spill the beans. If you don’t tell, then you might accidentally find out — or worse, you might not be able to find out at all.

The ultrasound works by sending high-frequency sound waves that are used to produce images of what’s inside you. You may not be able to recognize much of what you see, but the technician is trained to interpret the images. On most sonograms, the image is grainy black and white. The transducer — the part of the machine they rub on your belly (wand) — is moved around almost constantly, and the baby is swimming around too. (You wouldn’t be the first mama-to-be who thought she’s expecting, not a human baby, but an alien one.)

Ultrasound cheat sheet

Spine

Some moms think the baby’s tiny spine looks a lot like a string of pearls — lots of little tiny bones in a line. It reminds me of the spine of dinosaur skeletons you see in natural history museums.

Girl or boy?

Girl parts look like three lines, while a boy part often appears pretty much as you’d expect. Be sure not to confuse the umbilical cord and the penis. You might get a surprise at birth if you try to interpret the scan on your own.

Little face

Waiting for the first glimpse of Baby’s face? The baby’s face will look a little spooky — like a skull mask — from certain angles. But it will seem super-cute if you see your little one sucking his or her thumb in-utero.

More to look for

Amniotic fluid will be one of the darker things on the scan, and the harder tissue — such as bone — will appear bright.

Preparing for the ultrasound

There really isn’t much to preparing for the ultrasound. Usually, the sonogram imaging specialists will ask you to have a full bladder (but then, what pregnant woman doesn’t feel like she has a full bladder?). Depending on how long you have to sit in the waiting room, you may want to bring a bottle of water so you can unload and refill while you wait so you aren’t too uncomfortable.

More: Mom-to-be sees dead grandmother in ultrasound image

Why does your bladder need to be full? When your bladder is full, it acts as a balloon, pushing the uterus up out of the pelvis a bit, which helps the tech see the baby, umbilical cord, amniotic sac, placenta and uterus.

Up next: What to wear

Originally published September 2012. Updated December 2016.