An ultrasound examination is a type of examination where one uses sound waves that have a higher frequency than we humans can hear, unaided. These sound waves are sent through the surface of the skin into the soft body tissue, and then reflect back to the ultrasound machine, which interprets these signals, and converts them into a picture on the screen. That way, we can see an image of a fetus in the uterus, surrounded by amniotic fluids.

Is ultrasound dangerous?

There is no documentation indicating that properly administered ultrasound examinations are dangerous.

Ultrasound examinations have been used during pregnancies since the 1960’s. Nonetheless, it is the responsibility of the sonographer to ensure that the unborn child not be exposed to unnecessary risk, in connection with the use of high frequency energy.

Determining the baby’s due date

In Norway, a pregnant woman may take an ultrasound examination through the public health services during the 18th week of the pregnancy. At that time, ultrasound is used to:

  • determine the anticipated due date,
  • determine the placement of the placenta,
  • check whether there are several fetuses, and
  • check whether the anatomy of the fetus appears normal.

Research indicates that determining the due date by using ultrasound (TUL) is more reliable than calculating the due date based on the first day of the last menstruation (Naegele’s Rule).


Measuring growth of the fetus can be done at any time after the 24th week of a pregnancy.

When calculating fetal weight, it is necessary to use the due date which has been determined during the regular examination. Based on that benchmark, one can determine whether the fetus weighs more or less than average. In order to comment on how the child is growing, it is necessary to take several measurements over time.

If there is reason to suspect any illness or defect, you will be referred to the hospital.