High frequency sound waves are used to obtain images of the unborn baby and the different structures of the baby. These sound waves pass through a device known as tranducer, which then pass through the amniotic fluid surrounding the baby and bounce off the baby harmlesly, creating “echoes”. These “echoes” are converted into images by the computer and screened on the monitor so that the outline of the baby and the internal structures can be seen. Currently, the equipment used are known as real-time scanner, whereby continuous image of the moving fetus can be seen on the monitor screen. It has become a very useful diagnostic tool during pregnancy.
Ultrasonography for pregnancy :
- Confirm pregnancy
As early as five weeks of gestation, the gestational sac can be seen on an ultrasound. At six weeks, the embryo can be measured and observed. The scan also helps to confirm the number of babies.
- Determine age and size of fetus
Measurements of different part of the body reflect the age and size of the fetus. This is particularly important in early gestation. In patients with uncertain last menstrual periods, such measurements must be made as early as possible in pregnancy to arrive at a correct dating for the patient (dating scan). During later part of pregnancy, these measurements help in assesing growth of the fetus (growth scan)
- Diagnosis of fetal malformation
Ultrasound scanning allows comprehensive surveys of the fetal anatomy to detect the presencen of structural anomalies of the brain, heart, kidneys, lungs, limbs and other organs. Physical abnormalities in the fetus and fetal organs can often be detected via ultrasound within 22 weeks of pregnancies (fetal anomaly scan)
- Placental localisation
An ultrasound scan is very useful in identifying the site of the placenta. This assists the physician in excluding a placenta praevia (placenta lying close to the neck of the womb) and other placental abnormalities.
- Doppler blood flow studies
This is a special type of scan which allows the physician to study in great details the blood flow to various fetal organs and the placenta.
- Other diagnosis
Ultrasound scan can be used to confirm fetal presentation, evaluate fetal movements, tone and breathing, determine the fetal gender and diagnose uterine and pelvic abnormalities during pregnancy such as fibroids and ovarian cyst.
Types of ultrasound scan
- Transvaginal : Scan is done through the vagina
- Transabdominal : Scan is done through the mother’s abdoment