What is a fetal ultrasound?
Fetal ultrasound uses reflected sound waves to provide an image
of a fetus and
placenta within the uterus. Fetal ultrasound is the
safest way to obtain information about the fetus, such as size and position.
A fetal ultrasound can be done as early as the fifth week of
pregnancy. During the test, a small handheld instrument called a transducer is
used to direct sound waves toward the body. A computer analyzes the sound waves
that are reflected back from structures inside the body and converts them into
an image. Fetal ultrasound can be done by moving the transducer across the
woman's abdomen (transabdominal) or by putting the transducer in her vagina
(transvaginal). After about the 11th week of pregnancy, almost all ultrasound
tests are done using the transabdominal method.
What information can a fetal ultrasound provide?
An ultrasound done before 20 weeks of pregnancy can give you
- Fetal condition, if vaginal bleeding or other symptoms of
miscarriage have raised concern.
- Fetal age and size (sex can often
be identified at around 20 weeks of pregnancy).
- The number of
- Some types of birth defects, such as a defect of
the spinal cord (neural tube defect), heart, abdominal
organs, or brain.
- The condition of the
placenta and the amount of
amniotic fluid around a fetus.
Ultrasound may raise concern about a possible problem without
necessarily offering a definite diagnosis. In such a case, other tests are used
to confirm ultrasound findings.
What would I do with information from a fetal ultrasound?
A normal ultrasound does not guarantee a healthy child. However,
ultrasound results can give you useful information.
- If your ultrasound doesn't show any fetal
problems, you can feel more reassured and relaxed during your pregnancy.
- If you learn that you are carrying more than one fetus, you and
your health professional can plan ahead for a healthy pregnancy and delivery.
For more information, see the topic
Multiple Pregnancy: Twins or More.
- If you
find out that the fetus has a problem, you, your partner, and your health
professional can discuss your options. The first step may be to repeat the
ultrasound or have other tests that can confirm the results.
- Some problems are treatable soon after
the baby is born and may not seriously affect the baby's life. You may be able
to plan your delivery in a hospital that offers specialized care for sick
- Some defects, such as certain types of
neural tube defects and
Down syndrome, may not be fatal but will affect the
baby for his or her entire life.
- Rarely, a defect is so severe that
the fetus may not survive the pregnancy or may die soon after birth.
- Sometimes a possible defect is suspected but
not confirmed, and the baby is born perfectly healthy.
The decision about what to do if you find out that you are
carrying a fetus with a severe defect is very personal. Some women who learn
that they are carrying a fetus with a serious defect choose the option of
ending the pregnancy with a therapeutic abortion. Others make plans for raising
a sick or disabled child.
What are the risks of fetal ultrasound?
Fetal ultrasound is a very safe test and does not seem to have
any risks. However, an abnormal ultrasound can cause a lot of stress and
anxiety. An ultrasound:
- Can show an unusual result that requires more
tests, such as another ultrasound or
amniocentesis, to confirm. In most cases, these
additional tests are normal. However, the additional tests may carry risks.
Amniocentesis has more risks than ultrasound, including a very small risk of
- Can show an abnormality that disappears later in the
- May indicate a serious problem when there isn't one. In
such a case, additional tests are needed before you can know that there is not
a problem. It can be very stressful while you wait for the results.
What are the risks of not having a fetal ultrasound?
If you don't have an ultrasound, there is a slight chance that
you may not find out until later in the pregnancy or delivery that:
- You are pregnant with more than one fetus.
- A birth defect is present. Rarely, a fetus has a birth defect that
is so serious that the fetus will die later in the pregnancy, during delivery,
or soon after birth. Some women would choose to end a severely affected
pregnancy rather than suffer a stillbirth or death of a newborn.
For more information, see the topic