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Q&A: 4D ultrasound and fetal sentience

This Q&A page provides the O&G perspective on 4D ultrasound and whether images tell us about fetal sentience. It was published by the RCOG in May 2008 to accompany the passage of the Human Fertilisation and Embryology Bill through Parliament.

How is ultrasound used in obstetrics and fetal medicine?

Ultrasound scans are performed during the antenatal period to check on the progress of the developing fetus.

Two routine scans are conducted:

  • Early pregnancy scan (between 10 and 13 weeks): used to help date the gestational age of the fetus and to determine if the mother is expecting a single or multiple pregnancy
  • Second scan (between 18 and 20 weeks): used to check for physical abnormalities in the fetus

In some cases, later scans are carried out to assess the growth and progress of the fetus if the pregnancy is complicated by medical conditions such as high blood pressure or diabetes, or if there are concerns about the fetus’ wellbeing.

What about 4D ultrasound scanning – how does it differ from traditional ultrasounds?

New 4D ultrasound scanning provides 3D images of the fetus. The images show the fetus moving in the womb in time. These images are of better quality than those obtained by routine ultrasound examination to study fetal developmental abnormalities. Doctors also use this technology to study fetal behaviour.

There is much said about 4D images of the fetus smiling. Are these facial expressions accurate?

4D images pick up minor movements of the fetus. Facial twitches which look as though the fetus is smiling or wincing are discernible. Physical movements such as stretching or kicking are noticeable. When we see these images, we attribute sentient qualities to the fetus.

So, is the fetus is in fact, kicking or sucking its thumb, or sticking its tongue out?

These movements in the fetus are reflex actions. It may look as though the fetus is conscious about its movements but, in fact, these physiological functions are an involuntary response to stimuli inside the womb.

In other words, although it may look like the fetus is smiling, it isn’t. 4D technology and scanning are useful tools that help doctors to obtain a clearer picture of fetal growth and development. Our understanding of the significance of these activities is very limited.


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