Routine ultrasound examination of pregnant women

All pregnant women in Norway are offered an ultrasound examination around week 18 of their pregnancy. An ultrasound examination as part of prenatal care is a medical examination of the fetus and uterus.

Ung kvinne på ultralyd

Illustration: Doug Olson / Mostphotos

Ultrasound examination in brief

Ultrasound waves are high-frequency sound waves which are inaudible to humans. During the procedure, a probe is moved over the stomach of the pregnant woman which transmits sound waves into the uterus. The sound waves are reflected by the fetus, umbilical cord and placenta, and are reflected back to the probe, which detects them. The use of computer techniques helps produce detailed images of the fetus and take various measurements.

There has been no evidence of injuries to children caused by being examined with ultrasound as a fetus, but ultrasound is a medical examination and unnecessary use of it is not recommended.

Ultrasonic examinations usually take about half an hour. It is performed by a midwife with further education in ultrasound diagnosis. You can bring your partner or another companion with you. It is not recommended that you bring children to ultrasound examinations.

What does the ultrasound examination show?

Ultrasonic examinations involve a review of the fetus and uterus to obtain information about:

  • Age of the fetus and due date
  • Number of fetuses
  • Location of the placenta
  • Fetal development and anatomy

The gender of the fetus will not normally be of any medical significance and is therefore not routinely disclosed.

Age of the fetus and due date

The age of the fetus can be estimated from the date of the mother’s last menstruation. Using ultrasound enables the age of the fetus to be calculated more accurately based on measurements of the size of the fetus. It is important to determine the age and due date of the fetus as accurately as possible in order to assess fetal growth and development.

The age, due date and development of the fetus are vital factors in managing various conditions such as premature birth or overdue pregnancies.

A «full term» birth means that the baby is born during the period from 21 days before to 14 days after the due date. Approximately 90 percent of all women give birth during this period, and 6 percent of women give birth on the actual due date.

Number of fetuses

​The ultrasound examination shows whether there are one or more fetuses. Multiple pregnancies (pregnancies with more than one fetus) are monitored with additional ultrasound examinations to check on the growth and development of the fetus.

Location of the placenta

The ultrasound examination indicates where the placenta is located in the uterus. Placenta that remains around the birth canal or covers the birth canal completely (placenta previa) will prevent a vaginal birth.

If the placenta is observed close to the birth canal around week 18, you will have a further ultrasound examination later in your pregnancy.

In most cases, the distance from the placenta to the birth canal will increase as the uterus grows, making vaginal delivery possible.

Fetal development and anatomy

The ultrasound examination involves a review of fetal development and anatomy. Most fetuses develop normally. In some cases, the ultrasound examination can help to identify developmental abnormalities in the fetus. You will then be offered further investigations and monitoring by specialists in fetal diagnostics.

The person who performs the examination is obliged to inform you of any possible developmental abnormalities.