Genetics Northern California

Prenatal Ultrasound

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

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.

First trimester ultrasound: You will have an ultrasound during one of your early prenatal visits. The early ultrasound checks your due date and counts the number of fetuses. You may also be able to see a heartbeat.

Second trimester ultrasound: An ultrasound is done when you are about 18 to 22 weeks pregnant. This exam 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 is done by a doctor who specializes in prenatal ultrasound. It is scheduled when a routine scan suggests a possible concern with the fetus, or when part of the fetus is hard to see. A level 2 ultrasound is also offered when a screening test shows a high risk for a birth defect.

Risks: 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.

Results: Most prenatal ultrasound results are normal. Your doctor, nurse practitioner or nurse midwife will discuss your ultrasound results with you. Ultrasound has some limitations. Ultrasound cannot find all birth defects and it sometimes suggests a birth defect is present when it is not. You will be told about any ultrasound findings that need follow-up and you may be offered additional tests.

Click here for an information sheet on ultrasound in pregnancy: Ultrasound Exam in Pregnancy (pdf) [Spanish version]

Common ultrasound findings:

Last reviewed: August 2020
Reviewed by: Kimberly Barr, MS, LCGC   Kaiser Permamente NCAL Regional Genetics