What Happens During the 12-Week Ultrasound?

The 12-week ultrasound allows your doctor to check how your baby is developing and screen for conditions like Down syndrome. Your doctor can also determine your due date and how many babies you are carrying with this scan. The baby’s external genital organs are developed, so your doctor may be able to determine the sex of your baby as well.

Week 12 is the end of the first trimester of your pregnancy, which is when all of the major organs and body systems of your baby are forming. At week 12, the baby’s organs and body systems are fully formed. In most cases, the 12-week ultrasound may be the first time you see your baby.

a female doctor pointing at an ultrasound image of a baby

Marcus Chung / Getty Images

What Is an Ultrasound?

An ultrasound, or sonography, is an imaging method that uses the energy generated by sound waves to produce pictures of the inside of your body. During an ultrasound exam, a transducer sends sound waves into your body, which bounce back to produce a reading. Those waves then hit tissues, fluids, or bones inside the body. The signals bounce back and produce images that can help diagnose conditions or take measurements inside the body.

Purpose

The 12-week ultrasound allows your doctor to get a view of your baby inside the uterus. However, your ultrasound may not occur at exactly 12 weeks. Ultrasounds at 12 weeks are common, but not standard, because not enough development has taken place at this stage for your doctor to visualize your baby’s limbs and organs in detail.

In many cases, an ultrasound is done in the first trimester to confirm pregnancy and the number of fetuses (what a baby is called before eight weeks), as well as get a view of the baby’s overall development.

Importance

While your doctor will be limited in what they can see at this early stage of pregnancy, a 12-week ultrasound may be used to:

  • Estimate your gestational age and due date
  • Screen for certain disorders, such as Down syndrome
  • Count the number of fetuses
  • Check your baby’s heart rate
  • Rule out an ectopic pregnancy (when a fertilized egg implants outside of the uterus)

While most women usually have two ultrasounds—one around 12 weeks and one around 20 weeks—your doctor may perform just one. If only one ultrasound is performed, it will take place around the 20th week of pregnancy to:

  • Check the fetal position, movement, and heart rate
  • Estimate your baby’s size and weight
  • Check the amount of amniotic fluid in the uterus
  • Find the location of the placenta
  • Confirm the number of fetuses
  • Assess for abnormalities or birth defects

Nuchal Translucency Ultrasound Screening

The screening test for Down syndrome and two chromosomal disorders, trisomy 13 and trisomy 18, used at this stage of pregnancy is called a combined test. It involves a blood test and measuring the fluid at the back of the baby’s neck (nuchal translucency) with an ultrasound scan.

However, combined screening is not a diagnostic test, which means it cannot tell you whether your baby has Down syndrome, trisomy 13, or trisomy 18. Instead, the screening provides a probability that the baby might have one of these genetic disorders.

The probability, or chance, is based on three criteria: your age, information obtained on an ultrasound, and bloodwork. The screening results can either alert you and your doctor that your baby is at an increased risk for one of these chromosomal disorders or be reassuring that your baby is at a lower risk for these conditions.

A positive result that shows an increased risk does not mean that your baby has a problem, and a negative or normal result (one that shows a decreased risk) does not mean that the baby will not have a chromosomal abnormality.

The first-trimester screening’s detection rate is approximately 96% for pregnancies in which the baby has Down syndrome and is somewhat higher for pregnancies with trisomy 13 or trisomy 18. A nuchal translucency ultrasound can be performed without the bloodwork, but the detection rate is reduced to about 70%.

What Happens During the 12-Week Ultrasound?

Your doctor will likely perform a transabdominal ultrasound, which transmits waves through your abdomen. In some cases, a transvaginal ultrasound may be performed to capture more direct or detailed images. A scan usually takes 20 to 30 minutes to complete.

Transabdominal Ultrasound

During a transabdominal ultrasound, you will be asked to lie down on an exam table—either in a procedure room or your doctor’s office—with your abdomen exposed from your ribs to your hips. You may be asked to arrive to your appointment with a full bladder, which will create a window to the womb area.

When the test is ready to begin, your doctor will apply an ultrasound gel to help conduct the sound waves to your skin. This will help improve the quality of the images produced by the ultrasound. Your doctor will then move a handheld ultrasound transducer back and forth across your abdomen using a small amount of pressure. This should not be painful, although you may experience some discomfort related to positioning.

They may pause over certain areas of your abdomen to capture specific images or measurements. Measurements will be taken from different sections of the baby’s body and your uterus. A short recording may be captured of your baby’s heart movement.

Transvaginal Ultrasound

During a transvaginal ultrasound, you will be asked to undress from the waist down, or you may even be asked to remove your clothing and wear a hospital gown. Unlike the transabdominal ultrasound, you will be asked to empty your bladder before the test begins.

When you are ready to begin the test, you will be asked to lie down on an exam table with your feet in stirrups, much like you would for a pelvic exam. A wand-shaped transducer covered in a protective sheath will be inserted through the vagina for an internal view of the uterus. This should not be painful, but you may feel discomfort as you would during a pelvic exam.

You may be given some initial information about your baby at the time of your ultrasound exam, but a detailed report will likely come afterwards, once it is examined by a radiologist. Your doctor will then discuss the results with you.

Additional Ultrasounds

While the above describes a standard 12-week or first-trimester ultrasound, there may be reasons for your doctor to request additional scans. If you experience bleeding or other concerning symptoms, your doctor may order a limited ultrasound to quickly check for a specific issue. This could occur at any point during your pregnancy.

You may also be asked to undergo a specialized ultrasound or have more regular scans performed. These ultrasound scans are conducted in the same manner as the 12-week ultrasound, but may examine the fetus in closer detail, with three-dimensional imaging or more frequently throughout your pregnancy.

A Word From Verywell

Many expectant parents look forward to their first ultrasound. It can give you the first glimpse of you baby and strengthen the bond with your unborn child. Two ultrasounds will be done in most pregnancies, but don’t be surprised if you only have one done—or more in a high-risk pregnancy. Resist the urge to have non-medical ultrasounds done as souvenirs of your pregnancy.

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Article Sources
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  1. American College of Obstetricians and Gynecologists. Ultrasound exams. Updated June 2020.

  2. Beth Israel Deaconess Medical Center. Ultrasounds during pregnancy: how many and how often? Updated September 18, 2018.

  3. Johns Hopkins Medicine. Combined first-trimester nuchal translucency screening.

  4. AIUM-ACR-ACOG-SMFM-SRU practice parameter for the performance of standard diagnostic obstetric ultrasound examinations. J Ultrasound Med. 2018;37(11):E13-E24. doi:10.1002/jum.14831