First trimester ultrasound examination is done to evaluate the presence, size, number and location of the pregnancy. Ultrasound can also be used for first-trimester sonographic genetic screening, as well as screening for any abnormalities of your uterus or cervix.
In the second or third trimester a standard ultrasound is done to evaluate several features of the pregnancy, including fetal anatomy. This exam is typically done between weeks 18 and 20 of pregnancy. However, the timing of this ultrasound might be altered 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 might be needed when a specific question requires investigation. Examples include the evaluation of fetal growth and the estimation of amniotic fluid volume. A specialized or detailed exam is done when an anomaly is suspected based on your history or other prenatal exam results.
Here are some of the reasons your health care provider might use fetal ultrasound:
- Confirm the pregnancy and its location. Some fetuses develop outside of the uterus, in the fallopian tube. A fetal ultrasound can help your health care provider detect a pregnancy outside of the uterus (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.
- 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. An ultrasound can help evaluate the placenta and amniotic fluid around the baby.
- Identify birth defects. An ultrasound can help your health care provider screen for some birth defects.
- Investigate complications. 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. Most babies are positioned headfirst by the end of the third trimester. That doesn't always happen, though. Ultrasound imaging can confirm the baby's presentation so that your health care provider can discuss options for delivery.
Fetal ultrasound should be done 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 an ultrasound can provide, share your wishes with your provider so that you can work together to determine what's best for you and your baby.
Sept. 19, 2015
- Frequently asked questions. Special procedures FAQ025. Ultrasound exams. American College of Obstetricians and Gynecologists. http://www.acog.org/Patients/FAQs/Ultrasound-Exams. Accessed Aug. 11, 2015.
- Shipp TD. Ultrasound examination in obstetrics and gynecology. http://www.uptodate.com/home. Accessed Aug. 11, 2015.
- Shipp TD. Basic principles and safety of diagnostic ultrasound in obstetrics and gynecology. http://www.uptodate.com/home. Accessed Aug. 11, 2015.
- Sfakianaki AK, et al. Routine prenatal ultrasonography as a screening tool. http://www.uptodate.com/home. Accessed Aug. 11, 2015.
- American College of Obstetricians and Gynecologists (ACOG) Committee on Practice Bulletins — Obstetrics. ACOG Practice Bulletin No. 101: Ultrasonography in pregnancy. Obstetrics & Gynecology. 2009;113:451. Reaffirmed 2014.
- AIUM practice guideline for the performance of obstetric ultrasound exams. American Institute of Ultrasound in Medicine. http://www.aium.org/resources/guidelines.aspx. Accessed Aug. 11, 2015.
- Avoid fetal "keepsake" images, heartbeat monitors. U.S. Food and Drug Administration. http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095508.htm. Accessed Aug. 11, 2015.
- Frequently asked questions. Pregnancy FAQ155. Ectopic pregnancy. American College of Obstetricians and Gynecologists. http://www.acog.org/Patients/FAQs/Ectopic-Pregnancy. Accessed Aug. 11, 2015.
- Frequently asked questions. Pregnancy FAQ098. Special tests for monitoring fetal health. American College of Obstetricians and Gynecologists. http://www.acog.org/Patients/FAQs/Special-Tests-for-Monitoring-Fetal-Health. Accessed Aug. 11, 2015.
- Cope J. Prenatal cardiac abnormalities: Screening, evaluation, and pregnancy management. http://www.uptodate/home. Accessed Aug. 11, 2015.
- Ghidini A. Chorionic villus sampling. www.uptodate.com/home. Accessed Aug. 11, 2015.
- Ghidini A. Diagnostic amniocentesis. http://www.uptodate.com/home. Accessed Aug. 11, 2015.
- Whitworth M, et al. Ultrasound for fetal assessment in early pregnancy (review). Cochrane Database Systematic Review. http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD007058.pub3/abstract Accessed April 22, 2015.
- Safety of ultrasonography in pregnancy: WHO systematic review of the literature and meta-analysis. Ultrasound Obstetrics and Gynecology. 2009;33:599.
- ACR–ACOG–AIUM–SRU practice parameter for the performance of obstetrical ultrasound. Amended 2014. American College of Radiology. http://www.acr.org/Quality-Safety/Standards-Guidelines/Practice-Guidelines-by-Modality/Ultrasound. Accessed April 22, 2015.
- Fetal imaging: Executive summary of a joint Eunice Kennedy Shriver National Institute of Child Health and Human Development, Society for Maternal-Fetal Medicine, American Institute of Ultrasound in Medicine, American College of Obstetricians and Gynecologists, American College of Radiology, Society for Pediatric Radiology, and Society of Radiologists in Ultrasound Fetal Imaging Workshop. Obstetrics and Gynecology. 2014;124:836.
- AskMayoExpert. Prenatal screening and diagnostic testing. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2014.