Seeing your baby on the screen for the first time is a moment most parents remember for the rest of their lives. But ultrasound is more than just beautiful images. It is a medical examination that provides important information about your baby's development and your health.

Most countries offer pregnant women two routine ultrasound scans as part of standard prenatal care. Here you will find out what happens at each appointment, what they look for, and how to prepare.

Routine Ultrasound Scans in Pregnancy

As part of standard prenatal care, most healthcare providers offer two routine ultrasound scans during pregnancy. These are voluntary, but the vast majority of parents choose to have them.

Early Ultrasound (Weeks 11–14)

In many countries, all pregnant women are offered an early ultrasound combined with a blood test to assess the risk of chromosomal abnormalities. This is commonly known as the combined first-trimester screening or NT scan.

What is checked:

Due date confirmed by measuring the baby's size (CRL – crown-rump length)
Number of fetuses (twins?)
Nuchal translucency – a measurement of fluid at the back of the baby's neck, which can indicate the risk of chromosomal abnormalities
Blood test (PAPP-A and free beta-hCG) analyzed together with the ultrasound measurements

The first-trimester screening gives a risk assessment, not a definitive answer. If the risk is assessed as elevated, further testing such as amniocentesis or chorionic villus sampling (CVS) may be offered. Talk to your midwife or doctor about what the results mean for you.

Anatomy Scan (Weeks 18–20)

This is the most comprehensive ultrasound during pregnancy. A thorough review of the baby's anatomy is carried out.

What is checked:

Baby's heart, brain, spine, and internal organs
Arms, legs, fingers, and toes
Position of the placenta
Amount of amniotic fluid
Baby's size and growth
Umbilical cord and blood flow

The examination usually takes 20–30 minutes, but may take longer if the baby is in an awkward position.

Want to know the sex? Most hospitals can tell you at the anatomy scan around week 18–20, but it is entirely your choice. Let the sonographer know before the scan begins whether you want to find out.

Week 20 Anatomy Scan: What Can You See?

The anatomy scan around week 18–20 is the most detailed ultrasound during pregnancy. A systematic review of the baby's body is performed — this is what many people refer to as the "big scan."

Anatomical Screening – Organ Review

The sonographer will spend 20–30 minutes going through the baby's anatomy point by point:

The Heart: The baby's heart is examined in detail. The sonographer checks that the heart has four chambers, that the walls between chambers are intact, and that the major blood vessels are correctly positioned. Congenital heart defects are the most common type of birth defect, and many can be detected on ultrasound — but not all.

The Brain: Brain development is assessed, including the two hemispheres, fluid-filled spaces (ventricles), and the cerebellum. These measurements provide information about brain maturation.

Spine and Spinal Cord: The entire spine is scanned to confirm that the spinal cord is closed (to rule out spina bifida).

Internal Organs: The stomach, kidneys, bladder, and diaphragm are checked. It is confirmed that the baby is swallowing amniotic fluid (visible in the stomach) and that the kidneys are producing urine (visible in the bladder).

Arms, Legs, Fingers, and Toes: All four limbs are measured and checked for normal development. The length of the femur (thigh bone) is used as a measure of the baby's growth.

Face: The lips and palate are examined to rule out cleft lip and palate.

Sex Determination

Around week 18–20, it is usually possible to see the baby's sex. Most hospitals will share this information if the parents wish. Let the sonographer know at the beginning of the appointment whether you would like to find out.

Sex determination is not 100 percent certain — it depends on the baby's position and image quality. It can be confirmed at a follow-up scan if there was any uncertainty.

Placenta Position

The position of the placenta is noted. Normally the placenta sits at the top or side of the uterus. If the placenta is positioned low (near the cervix), this is called a low-lying placenta. Most low-lying placentas move upward as the uterus grows, and this is rechecked around weeks 32–34.

If the placenta completely covers the cervix (placenta previa), extra monitoring is required and it may affect how you give birth.

Amniotic Fluid

The amount of amniotic fluid is assessed. Too little or too much fluid can indicate various conditions, though some variation is normal. Abnormalities are followed up with additional ultrasound scans.

Baby's Size and Growth Measurements

The baby is measured at several points: head circumference, abdominal circumference, and femur length. Together these provide a weight estimate and show whether the baby is growing as expected. Around week 18–20, the baby typically weighs around 200–250 grams and measures approximately 14–15 cm from head to bottom.

Tip for the anatomy scan: Babies tend to be most active after you have eaten. Have a small snack 30–60 minutes before your appointment so the baby is moving and all structures are easier to see. If the baby is in an unfavorable position, you may be asked to take a short walk and come back.

How to Prepare for Your Ultrasound

Good preparation can make the examination easier and the images clearer.

Before the early scan (weeks 11–14):

You may be asked to drink water so your bladder is half full. A full bladder lifts the uterus and improves image quality early in pregnancy.
You do not need to fast.

Before the anatomy scan (weeks 18–20):

No special preparation is needed. The baby is large enough that good images are possible without a full bladder.
Wear clothing that is easy to lift or lower over your belly.

For both scans:

Bring your partner or someone you would like with you.
Prepare questions you want to ask.
Remember that ultrasound is voluntary. You decide what you want to be examined for.

What Happens During the Scan?

You lie on a bed and gel is applied to your abdomen. The gel may feel a little cold, but it is harmless. The ultrasound device sends sound waves through the abdomen, which reflect back and create images on a screen.

At the early scan (weeks 11–14), the examination is sometimes done vaginally. This gives sharper images when the baby is still small. The examination is not painful but may feel a little unfamiliar.

The sonographer will be focused and may seem quiet while measuring and checking. This does not mean anything is wrong. They will take time to answer your questions after completing their measurements.

Additional Ultrasounds During Pregnancy

Some pregnant women need more ultrasound scans than the two routine ones. This may be because of:

Twin pregnancy – requires more frequent monitoring
Gestational diabetes – to monitor the baby's growth
Concerns about the baby's growth – if the uterus is measuring larger or smaller than expected
Placenta position – if the placenta was low at the routine scan, it is checked again later
Previous complications in a pregnancy

Track your baby's development week by week with Babysential's pregnancy timeline. There you will find information about what happens in each week of pregnancy.

Limitations of Ultrasound

Ultrasound is a valuable tool, but it does not detect everything.

Not all conditions can be identified. Some heart defects and other abnormalities can be difficult to see.
Image quality is affected by the baby's position, the amount of amniotic fluid, and the mother's body type.
A normal ultrasound is not a guarantee that everything is perfectly normal — but it does provide a great deal of useful information.

Ultrasound is considered safe for both mother and baby. It uses sound waves, not radiation.

When Should You Contact Your Healthcare Provider?

Between scheduled ultrasounds, contact your midwife or doctor if you experience:

Bleeding
Severe abdominal pain
Reduced fetal movement (from around weeks 24–26)
Fluid leaking from the vagina

If you notice fewer movements than usual from your baby after week 24, contact your labor and delivery unit for assessment. Trust your own experience — you know your baby's patterns best.

Frequently Asked Questions

Is ultrasound safe for the baby?

Yes. Ultrasound uses sound waves and is considered safe during pregnancy. There are no known side effects from the routine scans offered as part of standard prenatal care.

Can I decline an ultrasound?

Yes. All pregnancy examinations are voluntary. You decide what you want to be examined for. Your midwife or doctor can provide information to help you make the choice that is right for you.

What if they find something abnormal?

If something deviates from normal, you will receive information and may be offered further testing. You will be referred to a specialist if needed. Keep in mind that many findings are completely harmless and resolve on their own.

Prenatal Appointments – Complete Overview – everything about checkups during pregnancy
Track your pregnancy week by week – Babysential's pregnancy timeline
Pregnancy checklist – everything you need to do before birth
Overdue pregnancy – what happens after week 40?

Ultrasound During Pregnancy – What Happens at Your Appointments?