16-Week Ultrasound: What to Expect and What You'll See (2024)

Pregnancy is an exciting time. You’re growing a little human, anxiously awaiting their arrival, and preparing for a new chapter in your life. It can be overwhelming!

One constant should be a series of predictable milestones in your prenatal care.

Specifically, ultrasounds are key moments when you can get a glimpse at your growing bundle of joy while your doctor can confirm that the pregnancy is progressing properly or pinpoint any critical issues that might need to be addressed.

Let’s take a look at what you might expect at a 16-week ultrasound.

While it’s typical to have two ultrasounds during a standard pregnancy, you may have more — whether due to your own risk factors or your doctor’s desire to more closely monitor the baby’s progress.

A 16-week ultrasound isn’t standard — but don’t let it worry you! Look at it as an opportunity to get more glimpses of baby.

Your first ultrasound will usually occur between 8 and 14 weeks to listen for a heartbeat to confirm that you’re pregnant and to estimate a due date.

Then the next ultrasound is typically between 18 and 20 weeks. This ultrasound checks for overall fetal development and is sometimes called the “anatomy scan.”

But aside from the two standard ultrasounds, your doctor may schedule additional screenings to:

• do an initial check if you missed the earlier viability ultrasound
• more closely monitor your pregnancy if you’re at high risk of certain conditions
• check for multiples if they suspect you might be carrying twins, triplets, or more
• look for fetal conditions such as heart abnormalities, Down syndrome, or spina bifida
• address any complications you may be having, such as bleeding

There’s nothing you need to do to prepare for the 16-week ultrasound.

This transabdominal scan relies on a transducer that moves over your abdomen to display 2D images of your developing baby. It’s noninvasive and won’t hurt you or your baby, though it may cause you some discomfort if the technician needs to press down a little harder at times.

Expect the ultrasound to take anywhere from 30 to 60 minutes. During the procedure, your doctor or ultrasound technician — known as a sonographer — will:

• take measurements of your baby
• check the development of their spine
• reconfirm their heartbeat

This is all to ensure that everything is developing on track.

Depending on baby’s position, you might also be asked to move or turn so the technician can get a better look at different angles.

They’ll also check for fetal movement. So, don’t be surprised if your sonographer gently pokes your abdomen to encourage your baby to move if they’re not especially active during the appointment.

During the 16-week scan, you can expect to see a baby that is fully formed but just very small. But, if their development is on track, you should still be able to see arms, legs, fingers, toes, and even facial expressions during the ultrasound.

At this stage, if you want to know (and if baby cooperates with getting in the right position), your technician can also try to determine the sex of your baby as the genitalia should be fully visible in certain positions. However, this may require later confirmation.

At 16 weeks, your baby is usually between 4 and 5 inches long and weighs around 5 ounces.

During your 16-week appointment, your physician may measure your fundal height, though this is typically done starting at 20 weeks.

This noninvasive measurement checks the distance in centimeters from the top of your baby bump to the top of your pubic bone. This confirms that your baby is growing properly.

Usually, by the time you’re in your 24th week, your fundal height is the same number as your gestational week in your pregnancy. So, if you’re 27 weeks along, it’s assumed that you would have a 27-centimeter fundal height measurement.

However, there’s a margin of error in the measuring. It’s not uncommon for the numbers not to be a perfect match between your fundal height and your gestational week, especially before the 24th week — and this also has to do with the accuracy of your due date.

Your due date is an imprecise measurement its own margin of error. If you had an ultrasound early in your pregnancy to estimate your due date, it will be more accurate.

But all this to say: Don’t panic if baby is measuring a week or so off in either direction. It’s normal.

The 16-week ultrasound, if you have one, is also a critical period where your doctor will want to check for any potential developmental abnormalities. They do this by checking movement and measurements, as we mentioned.

While the 16-week appointment is noninvasive, your physician may also recommend that blood to be drawn to run a triple or quadruple screen for potential abnormalities like neural tube problems, Down syndrome, or additional chromosomal issues that can be screened by checking your blood.

This screening usually takes place between the 15th and 20th week, but screens conducted between 16 and 18 weeks are said to be the most accurate.

If those blood tests come back with results that indicate there may be an issue, your OB may then discuss more invasive diagnostic tests such as amniocentesis or chorionic villus sampling (CVS). Or they could recommend further noninvasive prenatal testing.

While amniocentesis and CVS are incredibly effective at confirming developmental abnormalities, they also carry tiny risks that can cause complications in the pregnancy such as miscarriage. So, physicians prefer to rely on noninvasive measures — like ultrasound — for initial screening.

If you don’t want to be surprised, you can also (usually) determine your baby’s sex during the 16-week ultrasound. Because your baby’s external anatomy is fully formed, it should be accurate.

But keep in mind that depending on how your baby is positioned, your physician or ultrasound technician may not be able to get a clear reading of their anatomy to confirm the sex.

If your sonographer isn’t able to get a clear reading, or if you have doubts, you can always ask your doctor to check the baby’s sex as part of a blood screening or have a later follow-up ultrasound to confirm.

Just like with people carrying one child, if you’re carrying twins, you can expect the 16-week ultrasound to show your babies in full detail.

However, don’t be surprised if your scan takes significantly longer, as your technician must be extremely detailed to ensure they’re taking the right measurements and properly labeling them for each child.

At this stage, your babies should each be about the same length and size as “singletons” — the medical term for a single-baby pregnancy.

However, many OBs use a different growth chart that’s catered to twins since twins and multiples are often smaller at birth when compared to babies from single births.

Also, don’t be surprised if one twin is slightly smaller than the other, because this is very common — only a large discrepancy is considered cause for concern.

The 16-week ultrasound is often your first serious glimpse at your baby. This exciting milestone helps to ease anxiety and makes the whole pregnancy experience even more real.

While noninvasive, this ultrasound is also an important step to screen for potential developmental abnormalities and to confirm that baby is growing properly.

While not every pregnancy will include a 16-week ultrasound, at some point between the 16- and 20-week gestation period, you’ll likely complete this important step.