Its most important use however is to determine anomalies and genetic disorders in the foetus early on in pregnancy that gives time for the doctors and the expectant mother to think about corrective measures even while the baby is in the womb.
What more, it is even possible to predict the age and the gender of the baby early on in pregnancy, something which was impossible a few years ago. An ultrasound machine uses sound waves for scanning the abdominal area of a woman. The waves detect the foetus and produce a scanned image called sonogram.
By measuring the sonogram, the technician can predict the age and the development of the baby, almost accurately. By looking at the images onscreen, you can also understand and the baby’s movements, facial expressions and much more.
Ultrasound machines have become very advanced now that even a 3 D and 4 D images are possible now where a very realistic foetal image can be seen inside the womb of the mother. Ultrasounds are completely safe for the baby and the mother.
Process of Ultrasound Scanning
For a pregnant women, the two basic types of ultrasound scan processes are used for measuring the baby’s development and also to detect abnormalities; transvaginal and abdominal. A transvaginal scan is done during the early stages of pregnancy when the foetal movements are difficult to detect with a transducer on the abdomen. It offers some inconvenience to the mother as the probe has to be inserted into the vagina for the procedure.
An abdominal scan is pretty much easy as the transducer is rolled on the abdomen for detecting the foetus. Abdominal scans are done in the later stages of pregnancy. Both have the same procedure of detecting the foetus apart from this physical difference.
Measurement From the Crown to the Rump (CRL)
The measurements taken during an ultrasound scan is used to determine how many weeks the baby is. For this the most important measurement considered is the measurement from the crown of the head to the rump. This measurement can be taken from the seventh week of your pregnancy until the thirteenth week during the first trimester.
The measurement taken from the crown to the rump helps the doctor in determining the gestational age of the baby by calculating the number of weeks that corresponds to the growth. This will also help her decide an expected date of delivery. This is probably the first ultrasound scan that you undertake and hence an exciting time for you to see the foetus which is very small at this time yet with his heart beating rhythmically.
Measurement of the Circumference of the Head
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The circumference of the diameter of the head can be taken after the thirteenth week. This measurement can give a better idea to the obstetrician about the gestational age of your foetus and determine his normal development according to the number of weeks passed. The head circumference is measured from one side of the head to the other side.
The head circumference cannot however help in deciding the due date of the baby as all babies have varying head circumference at different weeks of their growth. A smaller than normal head circumference could mean that your baby is not growing according to the normal standards.
Measurement of the Leg Bone
The leg bone measurement which can be done early in pregnancy can help the obstetrician determine the gestational age of the foetus. This measurement is more accurate for predicting the expected date of delivery. Leg bone measurement or measurement of femur, the longest bone in the human body is done by clicking from one end of the bone to the other. This will give the length of the femur bone which will be noted at the side of the scan.
Measurement of the Foetal Abdomen
The foetal abdomen can be measured by measuring around the abdominal area of the foetus. The measurement of the abdomen can also predict the tentative date of delivery though this is not more accurate than measuring the weight of the foetus. Abdominal measurements are taken when you have not done a scan in the early part of your pregnancy.
Measurement of the Gestational Sac
The measurement of the gestational sac can be taken from the time the foetus is five weeks. Every day the overall size of the gestational sac increases by about a millimetre. The gestational sac is not uniform in size all over. However, taking an average measurement of the sac helps in predicting the expected date of delivery in most cases.
Figuring Out the Date of Conception Using Ultrasound Scan
For finding out the date of conception, an ultrasound done in the first trimester is the best way to go about it. Once the first trimester is completed, foetal growth is tremendous and varies considerably, making it difficult to identify the date of conception accurately. However, once the gestational age is identified in a scan, you can subtract 14 days from that date which will more or less give you the date of conception. This too is not an accurate observation as ovulation time differs in every woman.
However, on a general note, ovulation occurs any time after the tenth to the fourteenth day, starting from the first day of your menstrual cycle. Conception is possible one or two days after the ovulation process.
Calculate Your Due Date With CRL
To calculate the due date of your foetus, all you need to do is to take a look at your scan. The crown to rump length or CRL is the most obvious choice for calculating the due date. Take a gestational chart with normal values and compare the CRL of your foetus with the numbers and corresponding weeks in the chart. This way the current gestational age of your baby can be calculated.
Now you can subtract the gestational age of the baby that you have now from the average length of a pregnancy which is 280 days. The difference that you get can be added to the date of your ultrasound. This is you due date.
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