All infants should be screened at birth and during the early weeks-to-months of life for hip problems. Hip instability can lead to hip dislocation. The problem is called developmental dysplasia of the hip (DDH).
X-rays are the easiest and most common way to confirm the diagnosis. Your concern about exposure to radiation is understandable. Ultrasound (US) may be an acceptable alternative test.
US uses sound waves to give a picture of the soft tissue and bony structures of the hip. You may have already had an ultrasound of the baby when you were pregnant. Exposure to sound waves is not harmful and there is no radiation involved.
There are some drawbacks in using US for this type of exam. Sometimes it doesn’t show a problem that is really there. This is called a false negative result. There are many reports of dysplasia seen on US that resolve or go away without treatment.
Some experts advise further testing is needed with US before recommending its use routinely. Talk to your physician about your concerns and ask about the possible use of US. He or she will be able to answer any questions you may have and advise you.