Pregnancy Stages: What Is The 20-Week Ultrasound For?

One of the main milestones of pregnancy is reaching the date of your 20-week ultrasound. This is a routine ultrasound for pregnancy, and it's often when parents find out the sex of their baby. It's very exciting to know whether you'll have a boy or a girl, but it's also exciting to know what they look for in the ultrasound. If you're curious about the details of your 20-week sonogram, this guide can help you understand what to expect.

Normal Growth

The first order of business is to make sure that the baby is within the normal growth range for its gestational age. The ultrasound tech will measure the head circumference, the length of the spine, and size of the arms and legs. If your baby looks too small, your doctor will investigate to make sure your due date is correct or check for conditions which might be limiting the growth of the baby during gestation. 


One of the main reasons why a 20-week ultrasound has become routine is because it is quite effective at checking for serious health problems and birth defects. Some of these health problems can be life-threatening for the fetus, and a baby might require immediate surgery after birth. Knowing about potential problems before birth can help parents prepare for additional medical costs and learn about conditions before their child is born, or doctors can advise on whether the pregnancy should continue based on the prognosis of the current fetal development. Common anomalies that are normally found during a 20-week scan include:

  • heart defects. The tech can look at the valves and chamber of the heart to see if they are all present and working.
  • head size and shape. Some babies can have hydrocephalus or anencephaly -- where the head has too much fluid, or a portion of the head is missing. The development of the heard can also indicate genetic defects like Down syndrome that will require further screening to fully diagnose. 
  • spinal problems. Spinal bifida is almost always detected on the scan.
  • gastrointestinal problems. Sometimes, the abdominal wall does not form properly, allowing the intestines or liver to protrude outward. 
  • cleft lip. A cleft palate is still hard to detect on ultrasound, but a cleft lip on the infant's face is usually apparent.
  • missing or poorly formed kidneys. 
  • missing limbs. You ultrasound tech will also look for fingers and toes. 
  • chromosomal abnormalities like Edward's syndrome.
  • bladder problems. Your baby will already be urinating, and your tech can watch this happen on the sonogram.

All of the above conditions are the exception, not the rule. You should not feel nervous going to your ultrasound. Remember that it is best to discover if your baby is healthy and progressing in the pregnancy. 


Another purpose for the ultrasound is to help ensure your own health during the rest of your pregnancy and during delivery. The ultrasound tech will check the location of your placenta. Usually, this is just for interest sake, but sometimes the position of your placenta can indicate a more high-risk birth scenario. A low lying placenta that partially covers the cervix should be monitored into the third trimester. If the placenta is still covering your cervix near your due date, you'll be scheduled for a c-section to prevent severe bleeding and labor complications. Your doctor may also put you on bed rest or partial bed rest to prevent any premature bleeding from placenta previa

For more information on your 20-week ultrasound, contact your OBGYN. They should be able to answer any specific questions or address any concerns you might have about your pregnancy. And visit a site like for more information on ultrasounds.