Obstetric ultrasonograph of a healthy female fetus at 16 weeks. The bright white circle center-right is the head, which faces to the left. Features include the forehead at 10 o'clock, the left ear toward the center at 7 o'clock and the right hand covering the eyes at 9:00. Obstetric ultrasonography is the application of medical ultrasonography to obstetrics. Here, ultrasound is used to visualize the embryo or fetus in its mother's uterus (womb). In some countries, routine pregnancy ultrasound scans are performed to detect developmental defects before birth, the perhaps most promising method uses a measurement of the nuchal translucency thickness ("NT-test").
All current evidence indicates that diagnostic ultrasound is safe for the unborn child, unlike radiographs, which employ ionizing radiation.
The sex of the baby can usually be determined any time after 16 weeks, often at the dating scan around 20 weeks into the pregnancy. This is also the best time to have a ultrasound done as most infants are the same size at this stage of development.
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