Ultrasound in pregnancy

What is an ultrasound?

Ultrasound is a technique that uses sound waves to study the internal parts of the body. High-frequency sound waves (20,000Hz and above), which are beyond the range of normal hearing are transmitted to the area that needs to be studied and the returning echoes are recorded. The technical term for ultrasound testing and recording is sonography. It is used widely in every branch of medicine and especially in gynaecology and obstetrics.

How is it done?

In this technique, high frequency sound waves are used to produce an image of the baby inside the woman’s womb. This allows the evaluation of the baby, its organs, movements etc. Ultrasound during pregnancy may be done by two ways – transabdominal and transvaginal. In the former, the instrument called a transducer is passed over the abdomen, while in the latter, the transducer is placed inside the vagina.

Is an ultrasound necessary?

Usually, two ultrasounds are recommended as a routine during pregnancy to monitor the baby’s development. Some of the uses of an ultrasound during pregnancy are:

• To determine whether the pregnancy is normal or complicated (ectopic pregnancy)
• To determine whether there is a single baby or twins
• To make sure whether the position of the baby is normal
• Estimate the size and weight of the baby
• To check the position and attachment of the placenta
• To check the baby’s heart rate and respiration
• To detect the amount of fluid in the amniotic sac
• To check the baby for any fetal distress
• For determination of any physical abnormality in the fetus like abnormalities of the lungs or kidneys.

An ultrasound to check for the growth of the baby is usually done in the second trimester, while that to check for the presence of more than one fetus is usually done between the 16th and 20th weeks. The sex of the baby can be determined after the 16th week of gestation, but sex determination is not permitted by law. In fact, most parents do not even wish to know the sex of the baby, preferring the surprise instead.

Who should have an ultrasound done?

Though ultrasounds are recommended in all pregnant women, they must be done especially in women who have a family history of complicated pregnancies, previous babies with abnormalities or who have a gynaecological problem like enlarged ovaries, pelvic infection etc. The treating gynaecologist usually determines when an ultrasound is required.

What preparation is needed?

No special preparation is needed for the ultrasound scanning. However, it may be easier for the doctor to see the baby and its organs if the mother’s urinary bladder is full. Thus, the mother may be asked to drink upto 6 glasses of water before the test and not to urinate until after the ultrasound is over.

Is the test harmful?

Ultrasound scanning is usually not harmful to the mother or the fetus.