Pregnancy tests (Ultrasound)

Ultrasound is used during pregnancy to check the baby’s development and to help pick up any abnormalities such as Down syndrome. Since the procedure can’t produce high quality images, any suspected abnormalities need to be confirmed with other tests. The ultrasound scan isn’t 100 per cent accurate, but the advantages of the test are that it’s non-invasive, painless and safe for both mother and unborn baby.

The information obtained from different reflections are recomposed back into a picture on the monitor screen (a sonogram, or ultrasonogram). Movements such as fetal heart beat and malformations in the feus can be assessed and measurements can be made accurately on the images displayed on the screen. Such measurements form the cornerstone in the assessment of gestational age, size and growth in the fetus.
A full bladder is often required for the procedure when abdominal scanning is done in early pregnency. There may be some discomfort from pressure on the full bladder. The conducting gel is non-staining but may feel slightly cold and wet. There is no sensation at all from the ultrasound waves. Currently used equipments are known as realtime scanners, with which a continous picture of the moving fetus can be depicted on a monitor screen. Very high frequency sound waves of between 3.5 to 7.0 megahertz (i.e. 3.5 to 7 million cycles per second) are generally used for this purpose.

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Uses of the ultrasound :
Ultrasound may be used at various points during pregnancy, including:

• First trimester : ultrasound performed within the first three months of pregnancy is used to check that the embryo is developing inside the womb (rather than inside a fallopian tube, for example), confirm the number of embryos, and calculate the gestational age and the baby’s due date.
• Second trimester : ultrasound performed between weeks 18 and 20 is used to check the development of foetal structures such as the spine, limbs, brain and internal organs. The size and location of the placenta is also checked. The baby’s sex can be established, if the parents wish to know.
• Third trimester : ultrasound performed after 30 weeks is used to check that the baby is continuing to grow at a normal rate. The location of the placenta is checked to make sure it isn’t blocking the cervix.

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The main use of ultrasonography are in the following areas:

• Hydramnios and Oligohydramnios

Excessive or decreased amount of liquor (amniotic fluid) can be clearly depicted by ultrasound. Both of these conditions can have adverse effects on the fetus. In both these situations, careful ultrasound examination should be made to exclude intraulterine growth retardation and congenital malformation in the fetus such as intestinal atresia, hydrops fetalis or renal dysplasia

• Multiple pregnancies

In this situation, ultrasonography is invaluable in determining the number of fetuses, the chorionicity, fetal presentations, evidence of growth retardation and fetal anomaly, the presence of placenta previa, and any suggestion of twin to twin transfusion.

• Placental localization.

Ultrasonography has become indispensible in the localization of the site of the placenta and determining its lower edges, thus making a diagnosis or an exclusion of placenta previa.

• Diagnosis of fetal malformation.

Many structural abnormalities in the fetus can be reliably diagnosed by an ultrasound scan, and these can usually be made before 20 weeks. Common examples include hydrocephalus, anencephaly, myelomeningocoele, achondroplasia and other dwarfism, spina bifida, exomphalos, Gastroschisis, duodenal atresia and fetal hydrops. With more recent equipment, conditions such as cleft lips/ palate and congenital cardiac abnormalities are more readily diagnosed and at an earlier gestational age

• Determination of gestational age and assessment of fetal size

Fetal body measurements reflect the gestational age of the fetus. This is particularly true 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.

• Vaginal bleeding in early pregnancy

The viability of the fetus can be documented in the presence of vaginal bleeding in early pregnancy. A visible heartbeat could be seen and detectable by pulsed doppler ultrasound by about 6 weeks and is usually clearly depictable by 7 weeks. Fetal heart rate tends to vary with gestational age in the very early parts of pregnancy. Normal heart rate at 6 weeks is around 90-110 beats per minute (bpm) and at 9 weeks is 140-170 bpm. At 5-8 weeks a bradycardia (less than 90 bpm) is associated with a high risk of miscarriage.

• Diagnosis and confirmation of early pregnancy

The gestational sac can be visualized as early as four and a half weeks of gestation and the yolk sac at about five weeks. The embryo can be observed and measured by about five and a half weeks. Ultrasound can also very importantly confirm the site of the pregnancy is within the cavity of the uterus.

• Other areas

Ultrasonography is of great value in other obstetric conditions such as:
• Confirmation of intrauterine death
• Confirmation of fetal presentation in uncertain cases
• Evaluating fetal movements, tone and breathing in the Biophysical Profile
• Diagnosis of uterine and pelvic abnormalities during pregnancy e.g. fibromyomata and ovarian cyst.

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Ultrasound procedure :
The procedure depends on the type of ultrasound used, but may include:

• Transabdominal ultrasound : sound waves pass very well through water. The sonographer uses your full bladder as a ‘porthole’ to your uterus, so you will have to drink plenty of water before the test. You lie down on an examination table or bed. Gel is applied to your abdomen (to provide better contact between your skin and the scanner) and the sonographer moves the scanner in various positions. Pictures are sent instantly to a nearby monitor. The sonographer may have to push quite firmly at times in order to see the deeper structures. The scan usually takes about 30 minutes.
• Vaginal ultrasound : in some cases, a transabdominal ultrasound can’t produce clear enough pictures. There may be too much air in your bowel, for instance, and air is a poor conductor of sound waves. In these cases, a slender scanner is inserted into your vagina. The scan usually takes about 30 minutes.

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3-D and 4-D Ultrasound
3-D ultrasound can furnish us with a 3 dimensional image of what we are scanning. The transducer takes a series of images, thin slices, of the subject, and the computer processes these images and presents them as a 3 dimensional image. Using computer controls, the operator can obtain views that might not be available using ordinary 2-D ultrasound scan. 3-dimensional ultrasound is quickly moving out of the research and development stages and is now widely employed in a clinical setting. A good 3-D image is often very impressive to the parents.

More recently, 4-D or dynamic 3-D scanners are in the market and the attraction of being able to look at the face and movements of your baby before birth was also enthusiastically reported in parenting and health magazines. This is thought to have an important catalytic effect for mothers to bond to their babies before birth. What are known as 're-assurance scans' and the rather misnamed entertainment scans have quickly become popular.

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When can an ultrasound determine the sex of the baby?
You may have an ultrasound between 18 to 20 weeks to evaluate dates, a multiples pregnancy, placenta location or complications. It may also be possible to determine the gender of your baby during this ultrasound. Several factors, such as the stage of pregnancy and position of fetus, will influence the accuracy of the gender prediction. To be 100% sure you will have an anxious wait until the birth.

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Ultrasound

What is Ultrasound?
There are many reaons to get an ultrasound. Perhaps you are pregnant, and your obstetrician wants you to have an ultrasound to check on the developing baby or determine the due date. Maybe you are having problems with blood circulation in a limb or your heart, and your doctor has requested a Doppler ultrasound to look at the blood flow. Ultrasound has been a popular medical imaging technique for many years.
Ultrasound imaging, also called ultrasound scanning or sonography, involves exposing part of the body to high frequency sound waves to produce pictures of the inside of the body. Ultrasound exams do not use ionizing radiation (x-ray). Because ultrasound images are captured in real-time, they can show the structure and movement of the body's internal organs, as well as blood flowing through blood vessels.

In ultrasound, the following events happen:

1. The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe.
2. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).
3. Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected.
4. The reflected waves are picked up by the probe and relayed to the machine.
5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second).
6. The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.

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What are some common uses of the procedure?
Ultrasound is a useful way of examining many of the body's internal organs, including but not limited to the:

1. Heart and blood vessels, including the abdominal aorta and its major branches
2. Liver
3. Gallbladder
4. Spleen
5. Pancreas
6. Kidneys
7. Bladder
8. Uterus, ovaries, and unborn child (fetus) in pregnant patients
9. Eyes
10. Thyroid and parathyroid glands
11. Scrotum (testicles)
    

Ultrasound is used to help physicians diagnose symptoms such as:

• Pain
• Swelling
• Infection

Ultrasound is also used to:

• Guide procedures such as needle biopsies, in which needles are used to extract sample cells from an abnormal area for laboratory testing.
• Image the breasts and to guide biopsy of breast cancer ( Ultrasound-Guided Breast Biopsy ).
• Diagnose a variety of heart conditions and to assess damage after a heart attack or other illness.

Doppler ultrasound images can help the physician to see and evaluate:

• Blockages to blood flow (such as clots)
• Narrowing of vessels (which may be caused by plaque)
• Tumors and congenital malformation

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The Ultrasound Machine
A basic ultrasound machine has the following parts:

• Transducer probe - probe that sends and receives the sound waves
• Central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe
• Keyboard/cursor - inputs data and takes measurements from the display
• Disk storage device (hard, floppy, CD) - stores the acquired images
• Printer - prints the image from the displayed data
• Transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe
• Display - displays the image from the ultrasound data processed by the CPU
  

Different Types of Ultrasound
The ultrasound that we have described so far presents a two dimensional image, or "slice," of a three dimensional object (fetus, organ). Two other types of ultrasound are currently in use, 3D ultrasound imaging and Doppler ultrasound.
Doppler Ultrasound
Doppler ultrasound is based upon the Doppler Effect. When the object reflecting the ultrasound waves is moving, it changes the frequency of the echoes, creating a higher frequency if it is moving toward the probe and a lower frequency if it is moving away from the probe. How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound measures the change in frequency of the echoes to calculate how fast an object is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.
3D Ultrasound Imaging
In the past two years, ultrasound machines capable of three-dimensional imaging have been developed. In these machines, several two dimensional images are acquired by moving the probes across the body surface or rotating inserted probes. The two dimensional scans are then combined by specialized computer software to form 3D images.
3D imaging allows you to get a better look at the organ being examined and is best used for:

• Early detection of cancerous and benign tumors

examining the prostate gland for early detection of tumors

looking for masses in the colon and rectum

detecting breast lesions for possible biopsies

• Visualizing a fetus to assess its development, especially for observing abnormal development of the face and limbs
• Visualizing blood flow in various organs or a fetus

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