The history of ultrasound is based in the sonar that was used by the worlds navies during World War 2. After the war, researchers began experimenting with sonar to see if it could be helpful in medical diagnosis. It was first used to detect cancers and other growths that needed medical attention. It wasn’t until the 1950s that the medical community recognized that sonar could be useful to take ultrasound pictures of stages of pregnancy.
Ultrasound is a series of very high frequency sound waves. These sound waves are of a frequency that can not be heard by humans, so they are not detected by the woman or the fetus. A tool called a transducer, which looks something like a stethoscope, is placed on a woman’s abdomen. The sounds go through her skin and bounce back off whatever they contact inside the abdomen, producing an image that resembles a fuzzy black and white photograph. These images have become the now familiar ultrasound pictures of stages of pregnancy.
The use of ultrasound became increasingly prevalent in the 1960s. By then, scientists had discovered that, if the sound waves were in motion, the Doppler Effect would produce more accurate pictures. The Doppler Effect is familiar to most people when they hear a horn coming toward them and then moving away. Since sound is different if it is coming or going, the technique was used to produce more accurate pictures. The technique also allows ultrasound pictures of stages of pregnancy to detect motion of the fetus.
By accident, it was learned that the best ultrasound pictures of stages of pregnancy were produced when the techniques was used on women with full bladders. The use of ultrasound has become a common practice in obstetrics and women usually enjoy seeing the first “pictures” of their infants.
Ultrasound pictures of stages of pregnancy are most common in the second and third trimesters of the pregnancy. By that point, the fetus is usually large enough that it can easily be detected. During the next several weeks, depending on the position of the fetus, it may be possible for a woman to discover not only the gender of her child, but whether or not she is carrying more than one child.
This information, however, is not infallible, as the pictures can be misleading in the earlier weeks of the second trimester. As the fetus grows and its organs, arms, legs, fingers, toes and head become more recognizable, it is easier to detect the gender of the child or children. The ultrasound pictures of stages of pregnancy also allow practiced physicians to detect any possible problems in the fetus.