The growth of a baby in the uterus is determined using ultrasound. This is a non-invasive imaging technique that uses sound waves to create images of the fetus inside the womb. Ultrasound works by sending high-frequency sound waves into the body, which then bounce back off the tissues and organs to create a visual representation. It allows healthcare professionals to monitor the baby`s growth, check for abnormalities, and ensure that everything is developing as expected. X-rays and gamma rays are not used to assess fetal growth as they can be harmful to both the mother and the developing baby. Ultraviolet rays, on the other hand, are not used because they cannot penetrate the body to create images.