When three-dimensional images are captured using ultrasonography, it is called 3D ultrasound. When these images are dynamic, including the element of time as the fourth dimension, it is called 4D ultrasonography.

Pregnancy confirmation is done through ultrasonography. Within four and a half weeks of the last menstrual period, the gestational sac in the uterus can be identified, and by five weeks, a smaller sac (yolk sac) inside the gestational sac can be seen to confirm pregnancy. The embryo becomes visible after five and a half weeks.

There is no fixed schedule for performing ultrasonography during pregnancy. It is done when there is any suspicion or problem. After seven weeks of pregnancy, the fetus and its heartbeat can be seen through ultrasonography. Between 11 and 14 weeks, the nasal bone and the nuchal translucency (fluid-filled space at the back of the neck) are examined to assess the risk of mental and physical abnormalities in the fetus. Between 18 and 20 weeks, structural defects of the fetus can be better understood. Around 32 weeks, the fetus’s growth, weight, and external condition are usually assessed.

If any anomaly was suspected in earlier scans, it is rechecked at this stage. The fetus’s gender can be determined after 24 weeks, but it is better not to disclose the gender unless there is a special medical reason. Many countries have laws prohibiting disclosure of fetal gender.

X-rays and CT scans use high-energy radiation that is harmful to the body. However, ultrasonography uses ultrasound waves, which have not been found to cause any significant harm so far. It is also important to note that having a good-quality machine and the skill of the person performing the scan are both crucial for accurate diagnosis. Since ultrasonography has no side effects, frequent scans during pregnancy are generally not recommended unless medically necessary. The test should be done only after consulting a doctor when there is a specific reason or need for information.