The test that most women look forward to — the ultrasound — gives you your first glimpse at your little one and lets your practitioner assess the baby's growth and development. It may also be used to diagnose placental abnormalities, an ectopic pregnancy, certain birth defects, or other suspected problems.

There are two types of ultrasound scans: the transabdominal, which scans through your abdomen, and the transvaginal, which scans directly into your vagina. In very early pregnancy, the technician may opt for the vaginal approach, which means that the transducer (or hand-held wand) will be inserted into your vagina. However, abdominal ultrasounds are the most common since most ultrasounds take place in the second or third trimesters.

What to Expect

An ultrasound typically takes no longer than a half hour to perform. If you are in the first half of your pregnancy, you will probably be instructed to drink plenty of water prior to the exam and refrain from emptying your bladder. This is probably the most difficult part of the test. The extra fluids help the technician to visualize your baby.

Once in the examining room, you will recline on a table or bed with your upper body elevated and your abdomen exposed. Ask for extra pillows if you tend to get woozy when not lying on your side. The lights may be dimmed to allow the operator to see the sonogram picture more clearly. A thin application of transducer paste, jelly, or oil will be spread on your abdomen and then the fun begins.

The ultrasound picture (or sonogram) is obtained when high-frequency sound waves are passed over your abdomen with a transducer. These waves bounce off the solid structures of your baby, sending back a moving image of the tiny being inside. The resulting picture is transmitted to a computer or television screen.

If your fetus isn't feeling coy on ultrasound day, a sonogram taken after sixteen weeks may reveal its sex. A sighting of a little girl's labia (visible as three parallel lines) or a boy's penis can provide a fairly positive ID, but keep in mind that ultrasound is not foolproof and parents have been surprised in the delivery room.

The ultrasound technician may take a series of measurements during the procedure using the computer attached to the ultrasound unit. These measurements help your provider assess the growth and organ development of the fetus. Depending on the timing of the test and the cooperation of your unborn child, the provider may also be able to get an idea of the gender. Typically, this information won't be given unless you ask for it, in case you prefer to be surprised at birth.

Once the test is over, the technician will help you clean the transducer gel off your belly and you'll be able to empty your bladder if need be. The ultrasound operator can print out pictures for you to take home, so if she doesn't offer, make sure you ask.

A level-two ultrasound uses the same technology as a regular sonogram but involves a more detailed analysis of the results. It is frequently performed by a perinatologist who is specially trained in its use. The doctor will check fetal growth, organ system development, position of the placenta, and amniotic fluid volume. There are a number of reasons for a level-two to be ordered, from the routine to the potentially more serious. Your doctor should keep you informed, so if he hasn't given you a reason, ask.

Advances in Ultrasounds

Ultrasound pictures are typically a grainy black and white, but newer three-dimensional ultrasound technologies on the market can display your child in living (but simulated) color and are incredibly lifelike. The two-dimensional units are more common, however, in part because they are much less expensive.

The newest wave in ultrasound — four-dimensional technology — is actually 3-D with movement added. The picture is clearer, and the movement component allows for diagnosis of heart defects. It can also be used to check for markers of developmentally normal fetal movements.

Although an estimated 70 percent of pregnant women in the United States currently have at least one ultrasound, the ACOG does not currently support routine prenatal ultrasounds in low-risk pregnancies (except for specific medical indications). However, the routine use of ultrasounds is widespread outside of the United States.

When and if you have an ultrasound will depend upon your provider. Many obstetricians order ultrasounds as a matter of routine. Some do one at the first visit to check for correct dates and viability with the rationale that it may save them from questioning gestational dates later on (since dating is more accurate when done in the first trimester). Others will recommend a sonogram at around week 20 to examine the fetal anatomy and ensure the pregnancy is progressing normally.

A patient's peace of mind may also be reason enough to order an ultrasound. Since it is a noninvasive and fairly inexpensive test that can reassure the parents-to-be that matters are developing normally, many providers will comply with a woman's request for an ultrasound. If your doctor hasn't ordered one and you have some anxieties about your baby's health, it can't hurt to ask.

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