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An unseen world
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The ultrasound scan is a safe, non-invasive and an accurate obstetric tool
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PHOTO: SHAJU JOHN
MOTHER-TO-BE? Many physical abnormalities in the foetus can be reliably diagnosed by an ultrasound scan
Sumithra is excited. She is three months pregnant and has been scheduled for an ultrasound examination. She and her husband will actually be able to see the baby! At the same time she is nervous. Will the baby be normal? Does she have twins?
What is an obstetric ultrasound scan?
In the 70s, ultrasound scanning was introduced, to image the foetus growing inside the uterus. Ultrasound scans literally threw new light on the growing foetus, giving us a glimpse into the hitherto hidden world of the foetus.
Ultrasound scan is a safe, non-invasive, accurate and cost-effective investigation in a pregnancy. It has increasingly become an indispensable obstetric tool and plays an important part in the care of every pregnant woman.
The role of ultrasound scanning in pregnancy
Confirmation of pregnancy
Ultrasound can confirm a pregnancy by five weeks from the last period. By six weeks of pregnancy a heartbeat can be confirmed.
Diagnosing a miscarriage
When there is vaginal bleeding in early pregnancy, ultrasound examination is very important in confirming the viability of the foetus. If the heartbeat is identified, the chance that the baby will go to term is almost 95 per cent. In case the pregnancy is not growing well, the gestational sac may be irregular and the foetus may not be identified. This is called a blighted ovum. If the foetus is seen but there is no heart beat, a diagnosis of missed abortion
Occasionally, the pregnancy may not be growing inside the uterus but may actually have formed inside the tube. This is called an ectopic pregnancy.
Dating of pregnancy
Foetal body measurements give us the gestational age of the foetus. A scan done between six and 12 weeks of gestation will give us the most accurate age of the foetus. In the second half of pregnancy measuring body parameters will allow assessment of the size and growth of the foetus. The measurements help in determining if the baby is growing well or not.
Confirming that the baby is normal
Many physical abnormalities in the foetus can be reliably diagnosed by an ultrasound scan. A few abnormalities can be seen even in the early weeks of pregnancy but the best time to look for most defects is between 20 and 24 weeks of pregnancy. It is important to remember that even with the most advanced ultrasound technology; 15-20 per cent of foetal defects may be missed.
A ‘normal scan’ report is not a guarantee that the baby will be completely normal. Some abnormalities are very difficult to find or to be absolutely certain about.
Ultrasound scanning is invaluable in the diagnosis of twins. Ultrasound scanning is also used to monitor the growth of the twins.
Screening and diagnostic procedures
Ultrasound scanning is a very important part of screening for chromosomal abnormalities like Down syndrome. It can also assist in other diagnostic procedures in prenatal diagnosis such as amniocentesis, chorionic villus sampling and foetal blood sampling.
How often is a scan done?
An early scan may be done at seven - eight weeks to confirm pregnancy, exclude ectopic or molar pregnancies, confirm the presence of a heart beat and measure the crown-rump length for dating.
A scan between 11-14 weeks is useful and can be combined with blood tests to rule out Down’s Syndrome. A scan at 20-22 weeks is important to rule out foetal abnormalities. Growth can be assessed and placental position determined. Your obstetrician may ask for a scan in the third trimester to assess foetal growth and evaluate foetal size and weight.
Special ultrasound scans
Doppler ultrasound: This imaging technique is used to measure the flow of blood in the blood vessels of the placenta and the foetal blood vessels.
3-D ultrasound: This technology uses specially designed probes and software to generate three-dimensional images of the developing foetus.
Fetal echocardiography: This technology is extremely useful to assess the baby’s heart structure and function. This is used to help assess suspected congenital heart defects.
GITA ARJUN
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