Fetal Ultrasound

A fetal ultrasound is a test done during pregnancy that uses reflected sound waves to produce a picture of a fetus, the organ that nourishes the fetus (placenta), and the liquid that surrounds the fetus (amniotic fluid). The picture is displayed on a TV screen and may be in black and white or in color. The pictures are also called a sonogram, echogram, or scan, and they may be saved as part of your baby's record.

Fetal ultrasound is the safest way to check for problems and get information about your fetus, such as its size and position. It does not use X-rays or other types of radiation that may harm your fetus. It can be done as early as the 5th week of pregnancy. The sex of your fetus can sometimes be determined by about the 18th week of pregnancy.

A combination of screening tests using ultrasound may be done in the first trimester to look for Down syndrome. The integrated test uses an ultrasound measurement of the thickness of the skin at the back of the baby's neck (nuchal translucency) and the blood levels of free beta-HCG and a protein called pregnancy-associated plasma protein A (PAPP-A) to check for problems.

Different information is gained at different times (trimesters) during your pregnancy.

• First 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.
• Second 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.
  
  Third 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.
  

A fetal ultrasound can be done transabdominally or transvaginally.

Transabdominal ultrasound

You will lie on your back on a padded examination table. A gel will be spread on your belly.
A small, handheld instrument called a transducer will be pressed against the gel on your skin and moved across your belly several times. You may watch the monitor to see the picture of the fetus during the test.

Transvaginal ultrasound

A 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.

For a transvaginal fetal ultrasound, the vaginal transducer is usually covered with a latex sleeve and a vaginal lubricant, such as K-Y Jelly.

Ultrasound technologists are trained to gather images of your fetus but ordinarily cannot tell you whether it looks normal or not. The ultrasound images are reviewed by a radiologist or perinatologist and then communicated to you.