Fetal Ultrasound: Why It Is Done

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Why It Is Done

Fetal ultrasound is done to learn about the health of the fetus. Different information is gained at different times (trimesters) during your pregnancy.

• 1st-trimester fetal ultrasound is done to:
  • Determine how your pregnancy is progressing.
  • Find out if you are pregnant with more than 1 fetus.
  • Estimate the age of the fetus (gestational age).
  • Estimate the risk of a chromosome defect, such as Down syndrome.
  • Check for birth defects that affect the brain or spinal cord.
• 2nd-trimester fetal ultrasound is done to:
  • Estimate the age of the fetus (gestational age).
  • Look at the size and position of the fetus, placenta, and amniotic fluid.
  • Determine the position of the fetus, umbilical cord, and the placenta during a procedure, such as an amniocentesis or umbilical cord blood sampling.
  • Detect major birth defects, such as a neural tube defect or heart problems.
• 3rd-trimester fetal ultrasound is done to:
  • Make sure that a fetus is alive and moving.
  • Look at the size and position of the fetus, placenta, and amniotic fluid.

Transvaginal ultrasound is generally done early in a pregnancy to determine fetal age or to detect a suspected ectopic pregnancy. It is occasionally done late in pregnancy to determine the location of the placenta or in a high-risk pregnancy to monitor the length of the cervix.

Last updated:	June 28, 2007
Author:	Maria G. Essig, MS, ELS
Reviewed By:	Joy Melnikow, MD, MPH - Family Medicine, Deborah A. Penava, BA, MD, FRCSC, MPH - Obstetrics and Gynecology
Editors:	Susan Van Houten, RN, BSN, MBA, Tracy Landauer