Yes. For pregnant women, ultrasounds are safer than x rays because sonograms use sound waves, which do not affect the baby. On the other hand, ct scans and x rays use radiation, which do have risks to the unborn child at very high levels. Discuss this with your doctor.
Yes. Yes, ultrasound is safer than x-rays. The energy source for ultrasound is sound waves which has been established as safe in limited procedure times during pregnancy. X-ray energy source is radiation which has been established to be detrimental in higher doses to developing in utero babies.
Yes. Sound wave energy from ultrasounds are considered to be safe during pregnancies, but radiation energy from x-rays have been found to be detrimental to the developing fetus.