Ultrasound in Pregnancy

How doctors use the technology and what parents can learn from it.

Ultrasound images have revolutionized how doctors and midwives care for pregnant women, and how parents-to-be experience pregnancy.

This amazing technology can peer into the mother's body without exposing the mother or baby to harmful radiation, providing the doctor with a wealth of information that helps guide the care of the pregnant woman. And an ultrasound gives today's parents an opportunity never before available in human history: the chance to see their baby and begin to get to know him or her before the big arrival day.

At our medical practice, when we perform an ultrasound on pregnant patients, we are often asked about the role the technology plays in pregnancy. Following, we address some of the common questions that expectant parents pose.

1. How does an ultrasound look inside the body?

Ultrasound imaging, also called ultrasound scanning or sonography, uses high-frequency sound waves (at a pitch higher than humans can hear) to create images of structures within the body, such as the baby, placenta and umbilical cord inside a pregnant woman.

An ultrasound machine consists of a two-way microphone, called a transducer, that is attached to a computer. The transducer sends sound waves into the body and "listens" for echoes that return as the sound waves bounce back from organs and other objects inside the body. The returning pattern of echoes is translated by a computer into images and videos. The pictures can be of various types, including two-dimensional (2D), three-dimensional (3D) and Doppler ultrasound images. (See the sidebar on the following page for descriptions of these types of ultrasound.)

2. Is ultrasound safe?

The preponderance of scientific evidence indicates that ultrasound is safe. Unlike X-rays or CT scans, ultrasound does not use ionizing radiation, which can cause damage to cells— especially the cells of a baby growing inside the mother. Numerous professional organizations, including the American Institute of Ultrasound in Medicine, have concluded that there are no documented adverse effects of ultrasound on babies in utero, and that the benefits of ultrasound justify its use as a medical test for pregnant women.

3. Why do ultrasound in pregnancy?

There are many reasons why doctors and midwives use ultrasound on their pregnant patients. The reasons fall into two categories: scans done on women who are experiencing no problems to check that the baby is developing normally and scans done to assess a problem the mother is having.

The first type is called a routine scan, and many caregivers do two or three routine scans during a pregnancy. The first routine ultrasound is commonly done between 11 and 14 weeks of pregnancy. Also, it is often done in conjunction with a blood test on the mother. This scan toward the end of the first trimester determines whether the woman is carrying a single baby, twins or even more babies; checks for signs of chromosomal abnormalities such as Down syndrome; gives an accurate due date; and gets an initial look at the baby’s head, body, arms and legs.

A second routine ultrasound is often done between 16 and 18 weeks, when the baby has grown large enough for an ultrasound to be able to check that his or her organs and body parts are developing normally. In some cases, another routine ultrasound is performed in the third trimester to confirm the baby is growing appropriately.

When a problem arises during pregnancy, a doctor or midwife may perform an additional ultrasound to assess the problem and ensure the baby and mother are well cared for. For example, if a woman experiences vaginal bleeding during pregnancy, an ultrasound may be performed to try to identify the cause of the bleeding. Likewise, if a woman has cramping, ultrasound can be used to check that the cervix is still long and closed.

4. How can ultrasound improve a woman’s chance of a safe pregnancy and a healthy baby?

When ultrasound detects a problem, the information provided by the scan can often direct the doctor or other caregiver to initiate appropriate treatment that can improve the health, or even save the life, of the baby or mother. There are many ways in which this can happen; here are two examples:

-A 26-year-old woman, who had found out she was pregnant two weeks prior, went to her doctor because she was having pelvic pain. Her doctor ordered an ultrasound to look for the cause of her pain. Instead of showing a normal early pregnancy, the ultrasound demonstrated an ectopic pregnancy, meaning a pregnancy located outside the uterus, which can cause internal bleeding to the mother and can never result in a live-born baby.

The doctor then injected the woman with medicine to eliminate the ectopic pregnancy. Because the ectopic pregnancy had been picked up and treated at an early stage, the woman had none of the life-threatening internal bleeding that might have occurred if an ultrasound had not been done.

-A 32-year-old pregnant woman had a routine scan at 17 weeks of pregnancy, which showed that the baby’s kidneys were not draining urine to the bladder properly. Repeat ultrasounds every six weeks during the pregnancy showed that the problem persisted throughout the woman's pregnancy. This prompted the baby's pediatrician to prescribe antibiotics for the baby after he was born and to look at the baby's kidneys every two months with an ultrasound to monitor the situation.

An ultrasound of the baby at 10 months of age showed that the urinary drainage problem had resolved, and that the kidneys were becoming normal. The doctor discontinued the antibiotics and explained to the parents that, because ultrasound was routinely used in pregnant women, the rate of childhood kidney failure has been dramatically reduced as babies like theirs have received appropriate treatment right at birth.

Different Kinds of Ultrasound

Two-dimensional (2D) ultrasound images are cross-sections through the body, like slices through a loaf of bread. This type of ultrasound allows a doctor to see into a mother's body, as well as a baby's organs. This is the most commonly used form of ultrasound in pregnancy.

Three-dimensional (3D) ultrasound pictures show curved surfaces within the body, such as the outer surface of a baby inside a pregnant woman. This is the form of ultrasound that produces striking images of the baby's face, arms and legs that are most recognizable, and generally most exciting to parents. It can supplement a two-dimensional ultrasound to make sure that the baby is developing normally.

Doppler ultrasound images show blood flowing inside the body, such as the blood flow in the umbilical cord of a pregnant woman. When the computer inside the ultrasound scanner determines that there is moving blood in its field of view, it can produce images that show where blood vessels are located (color Doppler) or provide data about how fast blood is flowing (spectral Doppler).