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Pregnancy ultrasound

Definition

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.

How the test is performed

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.

How to prepare for the test

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.

How the test will feel

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.

Why the test is performed

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.

Normal Values

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

What abnormal results mean

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