Ultrasound is safe and painless, and produces pictures of the inside of the body using sound waves. Ultrasound imaging, also called ultrasound scanning or sonography, involves the use of a small transducer (probe) and ultrasound gel placed directly on the skin. High-frequency sound waves are transmitted from the probe through the gel into the body. The transducer collects the sounds that bounce back and a computer then uses those sound waves to create an image. Ultrasound examinations do not use ionizing radiation (as used in x-rays), thus there is no radiation exposure to the patient. 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.
Ultrasound imaging is a noninvasive medical test that helps physicians diagnose and treat medical conditions.
Obstetrical ultrasound provides pictures of an embryo or fetus within a woman’s uterus, as well as the mother’s uterus and ovaries.
A Doppler ultrasound study may be part of an obstetrical ultrasound examination.
Doppler ultrasound, also called color Doppler ultrasonography, is a special ultrasound technique that allows the physician to see and evaluate blood flow through arteries and veins in the abdomen, arms, legs, neck and/or brain (in infants and children) or within various body organs such as the liver or kidneys.
During an obstetrical ultrasound the examiner may evaluate blood flow in the umbilical cord or may, in some cases, assess blood flow in the fetus or placenta.
A probe is used to pass sound waves into the body. An image of the baby is produced by the reflection of those sound waves. The images (sonogram) are displayed on a television screen. The sonographer performing the ultrasound can explain these images to you.
Appropriate use of ultrasound poses no physical risk to you or your baby.
You may have an ultrasound to check the development of your pregnancy. This includes:
- Confirming the stage of the pregnancy;
- Checking the continuation of a pregnancy if there has been bleeding;
- Identifying a multiple pregnancy;
- Checking the position of the placenta;
- Checking the amount of amniotic fluid;
- Checking the physical development of the foetus; and
- Diagnosing birth defects and/or hereditary conditions.
A prenatal diagnostic ultrasound can detect physical abnormalities including:
- Congenital heart defects: Abnormalities of the structure and function of the heart occur in 1 in 100 pregnancies;
- Limb reduction defects: Short or missing bones in the arm or leg occur in 1 in 1000 pregnancies;
- Cleft lip palate:Failure of normal closure of tissue in the lip palate area occurs in 1 in 1000 pregnancies;
- Neural tube defects: Abnormalities of the brain, skull, spine and spinal cord (e.g. spina bifida) occur in 1 in 500 pregnancies
There are two ways in which obstetric ultrasound can be performed.
- Abdominal ultrasound is the most common procedure and can be used at any stage of pregnancy;
- A gel is applied to the abdomen to allow the sound waves to pass from the transducer into the uterus;
- The bladder should be comfortably full to gain a clear ultrasound picture.
In first trimester it is common for an ultrasound to be performed to confirm the gestation of the pregnancy. An ultrasound can be performed as part of a screening test at 11-14 weeks to screen for Down’s Syndrome. This screening test involves a blood test to measure two hormones, free B-HCG and PAPP-A, as well as an ultrasound scan. The ultrasound measures the nuchal translucency of the baby.
It is common medical practice to also offer an ultrasound scan, called the ‘foetal anatomy’ scan, at 18-20 weeks. This scan looks for the presence of physical abnormalities in the baby.
The ability to diagnose physical abnormalities depends on the equipment used, the position of the foetus, the stage of the pregnancy and the experience of the person performing the ultrasound.
- Most ultrasound scanning is noninvasive (no needles or injections).
- Occasionally, an ultrasound exam may be temporarily uncomfortable, but it should not be painful.
- Ultrasound is widely available, easy-to-use and less expensive than other imaging methods.
- Ultrasound imaging is extremely safe and does not use any ionizing radiation.
- Ultrasound scanning gives a clear picture of soft tissues that do not show up well on x-ray images.
- Ultrasound is the preferred imaging modality for the diagnosis and monitoring of pregnant women and their unborn babies.
- Ultrasound has been used to evaluate pregnancy for nearly four decades and there has been no evidence of harm to the patient, embryo or fetus.
- Nevertheless, ultrasound should be performed only when medically indicated.
- Ultrasound allows the doctor to see inside the uterus and provides much information about the pregnancy.