A fetal, or pregnancy, ultrasound uses high-frequency sound waves to create an image of your baby, your uterus and the placenta. Ultrasound can determine pregnancy, detect potential problems with a pregnancy or the baby and provide estimated conception and delivery dates. Near the end of pregnancy, ultrasound can determine if the baby is in an abnormal presentation and whether a Cesarean section might be necessary. Contact your doctor if you have questions about ultrasound or the results of your scan.
Timing
An ultrasound can determine pregnancy as early as five weeks, according to the U.S. Department of Health & Human Services. It can detect signs of Down syndrome or other developmental problems at nine to 13 weeks of pregnancy. Between weeks 18 and 20, an ultrasound can detect congenital malformations and, if you choose, tell you the sex of your baby.
Necessity and Risks
Many pregnant women have a routine ultrasound during the first trimester, to determine pregnancy, and another in the second trimester to detect abnormalities and the baby's sex. The American Pregnancy Association only recommends ultrasounds in the case of medical necessity, however, such as a high-risk pregnancy. Pregnancy ultrasounds are not entirely risk-free, but the Mayo Clinic considers routine scans safe for both mother and baby.
Procedure
A pregnancy ultrasound takes place when you are lying on your back. Your bladder must be full for the scan. The ultrasound technician spreads a gel that helps transmit the sound waves on your pregnant belly, then moves a transducer over the area. The transducer sends sound waves into your body, which bounce off bones and tissue back to the transducer and appear on the ultrasound screen as a black-and-white image of your baby and your innards. You might feel slight discomfort from the pressure of the transducer on your full bladder. The Mayo Clinic notes that a standard fetal ultrasound lasts about 20 minutes.
Types
Several variations of ultrasound exist, though the underlying process is essentially the same for each. A standard fetal ultrasound generates a flat, two-dimensional image of the fetus; 3-D and 4-D scans allow you to see the baby's face and movement in the womb. Transvaginal ultrasounds use a transducer inside the vagina, typically during early pregnancy when the uterus and Fallopian tubes are farther from the abdominal wall than in later weeks. If your doctor suspects a problem, a targeted ultrasound using advanced equipment can give you information that a standard ultrasound might miss. Fetal echocardiography looks at the baby's heart, and can detect or rule out congenital cardiac problems. Doppler scans detect slight changes in the ultrasound waves themselves as they reflect off moving objects like blood cells, and can give you information about your baby's circulation.
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