Most healthy women only get about two sonograms during pregnancy, according to the Beth Israel Deaconess Medical Center. A sonogram is the picture that is taken during an ultrasound. Typically one ultrasound is performed at some point during the first trimester and a second is performed at around 18 weeks.
The terms sonogram and ultrasound are often used interchangeably, advises the American Pregnancy Association, though they are not the same thing.
An ultrasound is used to determine the sex and track the development of the fetus. If there are any signs of medical problems with the fetus or mother, more ultrasounds may be required. Because the long-term effects of multiple ultrasounds aren't known, healthcare providers should only perform ultrasounds when medically necessary and not just to create keepsake sonograms.