First trimester ultrasound examination may be performed to evaluate presence, size, number and location of the pregnancy or for first-trimester sonographic genetic screening.

In the second semester ultrasound is typically performed to evaluate several features of the pregnancy, including fetal anatomy. The timing of this ultrasound may be altered in some women for reasons such as obesity or prior surgical incision at the scanning site, which could limit visualization of the fetus.

During the second and third trimesters, limited ultrasound evaluation may be indicated for evaluation of fetal growth, amniotic fluid, fetal well-being, confirmation of fetal presentation and placental abnormalities.

Here are some of the reasons your health care provider might use fetal ultrasound:

  • Confirm the pregnancy and its location. Some embryos develop in the fallopian tube instead of in the uterus. A fetal ultrasound can help your health care provider detect a tubal (ectopic) pregnancy.
  • Determine your baby's gestational age. Knowing the baby's age can help your health care provider determine your due date and track various milestones throughout your pregnancy.
  • Confirm the number of babies. If your health care provider suspects a multiple pregnancy, an ultrasound might be done to confirm the number of babies.
  • Evaluate your baby's growth. Your health care provider can use ultrasound to determine whether your baby is growing at a normal rate. Ultrasound can be used to monitor your baby's movement, breathing and heart rate as well.
  • Study the placenta and amniotic fluid levels. The placenta provides your baby with vital nutrients and oxygen-rich blood. Too much or too little amniotic fluid — the fluid that surrounds the baby in the uterus during pregnancy — or complications with the placenta need special attention.
  • Identify birth defects. An ultrasound can help your health care provider detect various birth defects.
  • Investigate signs or symptoms. If you're bleeding or having other complications, an ultrasound might help your health care provider determine the cause.
  • Perform other prenatal tests. Your health care provider might use ultrasound to guide needle placement during certain prenatal tests, such as amniocentesis or chorionic villus sampling.
  • Determine fetal position before delivery. A C-section might be needed if the baby is in an abnormal position.

Fetal ultrasound should be performed only for valid medical reasons. Fetal ultrasound isn't recommended simply to determine a baby's sex. Similarly, fetal ultrasound isn't recommended solely for the purpose of producing keepsake videos or pictures.

If your health care provider doesn't suggest a fetal ultrasound but you'd like the reassurance the exam can provide, share your wishes as you work together to determine what's best for you and your baby.

April 29, 2015