A pregnancy ultrasound is a method of seeing the fetus and female pelvic organs during pregnancy. The ultrasound machine sends out high-frequency sound waves. These waves bounce off body structures to create a picture.

You will lie down for the procedure. A clear, water-based conducting gel will be applied to your skin over your abdomen and pelvis. The gel helps transmit sound waves. A hand-held probe is then moved over the area.

Another method is performed with the probe placed in the vagina of the patient (transvaginal ultrasound scanning). This technique often complements conventional ultrasound techniques by providing better detail. Consult your health care provider to determine which technique is most appropriate for you.

A full bladder is necessary to get a good picture. Therefore, you may be asked to drink 2 to 3 glasses of liquid an hour before the test. You should not urinate before the procedure.

There may be some discomfort from pressure on the full bladder. The conducting gel may feel slightly cold and wet. You will not feel the ultrasound waves.

Some physicians order an ultrasound when an abnormality is suspected, while others advocate screening ultrasounds. You should consult your health care provider to determine the most appropriate scanning schedule for you.

Scans may be performed in the first trimester to:

• Confirm a normal pregnancy
• Assess the baby's age
• Rule out abnormalities, such as ectopic pregnancies or potential for miscarriage
• Assess the baby's heart
• See if there are multiple pregnancies
• Identify abnormalities of the placenta, uterus, and other pelvic structures

Scans may also be obtained in the second and third trimesters to:

• Assess the baby's age, growth, position, and sometimes gender
• Identify any developmental problems
• Rule out multiple pregnancies
• Evaluate the placenta, amniotic fluid, and remaining structures of the pelvis

Some centers are now performing a scan at around 13-14 weeks of pregnancy to look for risks for Down Syndrome (which causes mental retardation) or other developmental abnormalities in the fetus.

The total number of scans will vary depending on whether a previous scan or blood tests have detected abnormalities that require follow-up assessment.

The fetus and associated pelvic structures are normal in appearance and appropriate for the gestational age.

Abnormal ultrasound results may be due to some of the following conditions:

• Ectopic pregnancy
• Multiple pregnancies
• Fetal death
• Abnormalities of fetal position
• Congenital malformations
• Amniotic fluid problems, including oligohydramnios (not enough fluid) and polyhydramnios (too much fluid)
• Placental abnormalities, including placenta previa and placental abruption
• Intrauterine growth retardation
• Tumors of pregnancy, including gestational trophoblastic disease
• Additional abnormalities of the ovaries, uterus, and remaining pelvic structures

There is no documented effect on patients and their fetuses with the use of current ultrasound techniques. No ionizing radiation is involved.