Genetics Northern California

Prenatal Ultrasound

How this test is done 

    Ultrasound uses sound waves to make an image of a developing baby on a monitor.

Why this test is done
    Ultrasound is done during pregnancy to:

    • check your due date
    • find out if there is more than one baby (twins or triplets)
    • check the placenta and the baby
    • measure the fluid around the baby
    • monitor the baby's growth 
    • detect some birth defects
    • recognize when a miscarriage happens

    Ultrasound is also used to guide procedures like CVS and amniocentesis.

When this test is done
  • First trimester: You will have an ultrasound during one of your early prenatal visits. This scan checks your due date and counts the number of fetuses. You may also be able to see a heartbeat.
  • Second trimester: An ultrasound is done when you are about 18 to 22 weeks pregnant. This scan checks the growth and development of the fetus, the location of the placenta, and how much fluid is around the fetus (amniotic fluid). This ultrasound may also be able to predict fetal sex (boy or girl). 
  • Level 2 (targeted) ultrasound: This type of ultrasound may be scheduled any time during pregnancy when a routine scan suggests a possible concern with the fetus, or when part of the fetus is hard to see. It is also offered when a screening test shows a high risk for a birth defect. A level 2 ultrasound is done by a doctor who specializes in prenatal ultrasound. 

Test Results
    Most prenatal ultrasound results are normal. Your doctor, nurse practitioner, or nurse midwife will discuss the results with you. You will be told about any ultrasound findings that need follow-up and you may be offered additional tests.

    Ultrasound has been routinely used in pregnancy since the 1960s. There are no known health risks to the fetus or mother with routine use of prenatal ultrasound.

    Ultrasound cannot find all birth defects and it sometimes suggests a birth defect is present when it is not. 

Common ultrasound findings

Last Reviewed: March 2022
Reviewed by: Kimberly Barr, MS, LCGC   Kaiser Permanente NCAL Regional Genetics