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Over the last three decades, ultrasound as a technology used in the practice of medicine has come on in leaps and bounds. Today, ultrasound use in pregnancy care comes as a matter of course. Attitudes towards it differ from person to person, but the overall attitude is favourable. Nonetheless, there is always a certain amount of anxiety when it comes to the interaction of modern technology and pregnancy in particular. People rightly want to know what it actually involves, whether it is safe for them and their babies, why it is done in different ways, what the advantages are and a lot more besides.

It is always a good thing that pregnancy is allowed to be an enjoyable experience, considering what it is about. It is also important to emphasize that pregnancy is not a disease. It is a normal physiological process and the primary aim of ultrasound is to reinforce this point. In the few instances when it helps to identify something wrong, this should be looked at positively as it offers an opportunity of carrying out remedial measures, wherever possible. Here, we explain what ultrasound technology is all about.
What is Ultrasound?

Ultrasound is the form of sound waves generated at a very high frequency. The frequency used in these machines is in the range between 3.5 to 7 million cycles per second (Megahertz). Normal sound waves audible to the ear are produced at a frequency of only a few thousand cycles per second (hertz).

How does ultrasound work?
The sound waves produced by the crystal in the probe are reflected from the various structures they encounter as they travel. The different ways in which they are reflected are translated by the scanning machine into an image that is produced on a screen. The early scanners used to produce a static picture but, for many years now, these have been superseded by the so-called "real-time" scanners, where all movements taking place are visible.

How useful is the ultrasound in pregnancy?
It is not difficult for a contemporary obstetrician to wonder how earlier obstetricians managed without the ultrasound scan. It is virtually indispensable. Ultrasound is used to confirm the pregnancy, number of fetuses and gestation age, and detect all kinds of pregnancy complications.
Ultrasound: Uses in Pregnancy
What pregnancy complications can the ultrasound diagnose?
Fetal demise is one. From the gestation age of six weeks, the fetal heartbeat can be clearly seen on the ultrasound. Absence of this will indicate that the fetus is dead.

Growth restriction can be objectively identified, both by a single and by serial ultrasound scans. When the gestation age of the pregnancy is known with certainty (both from the last period and an early scan), a single ultrasound scan in the late phase of the pregnancy may confirm clinically suspected poor fetal growth. Alternatively, serial scans (done at least fortnightly) could objectively show that the rate of growth is below normal.

A great many fetal abnormalities - including those of the limbs, spine, face, brain, lungs, heart, bowel, kidneys, bladder, abdominal wall etc. can be detected by using ultrasound scanning. Other abnormalities, where the defect is very small, may not be seen.


At what gestation can the gross abnormalities be detected?
Most obstetric units operate a policy of performing scans at between eighteen and twenty weeks of gestation. (See the section: "Ultrasound scan at 18 to 20 weeks".) Earlier scans are likely to miss some abnormalities, as the fetus is still too small.



4. Ultrasound in Pregnancy

By Joe Kabyemela, MD

Early trimester Placenta and fluid 20 weeks scan Safety Uses in pregnancy Limitations 4D scans Fetal gender