Pelvic ultrasound scanning or sonography.

• To establish the age and number of fetuses, evaluate their size and well-being, determine the location of the placenta, establish the amount of amniotic fluid, and detect abnormalities in the fetus and mother's pelvis.
• To reveal fetal malformations and severe disorders such as spina bifida.
• If the baby is at risk of inheriting a sex-linked disease, to determine the sex of the baby.
• May be performed to monitor fetal growth in late pregnancy.
• To assist in other procedures, such as amniocentesis, CVS, and fetal blood testing, that require placement of a needle in the uterus.

High-frequency sound waves provide an image similar to an X-ray. The image, called a sonogram, shows the baby's entire body, organs, and the surrounding tissues.

• If the test is performed during the first trimester, you will be asked to drink a great deal of fluids beforehand (a full bladder descends, allowing a better view of the uterus, and the fluid is a good medium for transmission of sound waves).
• Later in pregnancy, this is not necessary because the amniotic fluid provides the medium, and the enlarged uterus not only pushes the bladder down but extends so that it lies directly against the abdomen.
• You can remain dressed but you will be asked to expose your abdomen.

• Gel is applied to your abdomen, and an ultrasound transducer is swept across the area.
• The tester observes the image displayed on the screen.
• The sonogram, printed on film, videotape, or paper, may later be examined more carefully (although the doctor may analyze the scan immediately during the procedure).

Transvaginal ultrasound: This technique uses a small ultrasound transducer (about the size of a tampon) that is inserted directly into the vagina rather than pressed against the abdomen. This eliminates the need for women to fill up on fluids beforehand. For this test you disrobe from the waist down and lie on your back on a pelvic-exam table. A sterile condom is slipped over the transducer, or probe, which is then covered with lubricating gel and placed in the vagina. (If you find this uncomfortable, which few women do, you can ask to insert it yourself.) The probe rests up against the cervix (see figure). This produces a much sharper image, not only because of the close proximity to the uterus, but also because the transducer's crystal can vibrate at a higher frequency. The rest of the test proceeds the same way as transabdominal ultrasound.

You are free to empty your bladder and return to previous activities.

• Obesity.
• Scars from abdominal surgery.
• In early pregnancy, a less-than-full bladder may obscure the results.

• A doctor examines the sonogram for structural abnormalities in the fetus, including congenital heart defects and bone deformities.
• The well-being of the fetus is evaluated by its movements and heart-beat.
• The doctor looks for problems in the mother, such as an incompetent cervix, which is prone to become dilated in pregnancy, leading to miscarriage.
• The sex of the fetus can be established around the 16th to 18th week of pregnancy.

• It entails no exposure to X-ray radiation.
• It's noninvasive.
• It produces quick results.
• It creates a moving image.

• It's less reliable than amniocentesis or CVS in diagnosing certain disorders, such as Down syndrome.
• False-positive and false-negative results are possible.

Suspected abnormalities should be confirmed at facilities with extensive experience at diagnosing fetal abnormalities.