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Different Types of Ultrasounds

To monitor the health of a fetus, sonograms are taken of the baby and placenta. To get a picture of the pelvic cavity, ultrasound (high-frequency sound waves) is used to scan the area. A computer program interprets the feedback to produce a picture (sonogram) on a monitor. The terms ultrasound and sonogram are used interchangeably in obstetrics to refer to this exam but the terms are technically different.

Different Types of Ultrasound

Although the basic procedures involved in ultrasounds are the same, there are several different types:

  • Standard Ultrasound – The most common type of ultrasound used in the medical community. A transducer is passed over the stomach to produce two-dimensional images of the baby.
  • Advanced Ultrasound – More specialized equipment is used during this exam to get a clearer view of problem areas. For example, if an unusual growth is spotted during a regular exam, an advanced ultrasound may be taken to determine what it is.
  • Transvaginal Ultrasound – This exam is typically done during the first few weeks of pregnancy when the fetus is too small to be seen using a standard ultrasound device. A probe is inserted inside the vagina to get images of the uterus. Since the ultrasound waves don’t have to cut through skin, fat or bone to reach the uterus, the images produced are usually clearer.
  • Doppler Ultrasound – Used to monitor movement, such as blood flow, this technology measures the changes in ultrasound waves as they bounce off objects in the body.
  • 3-D Ultrasound – A three-dimensional image of the fetus is produced using a specially designed probe and computer software.
  • Dynamic 3-D and 4-D Ultrasound – Typically used right before delivery, this type of ultrasound looks at the baby’s movements and face.
  • Fetal Echocardiography – If congenital heart defects are suspected, this type of ultrasound is used to look at the heart and monitor its function.

Ultrasound Procedure

An ultrasound technician will put a special gel on the stomach. This gel helps facilitate the sound waves. Using a transducer, the technician will transmit sound waves into the area. The sound waves bounce off tissue and bones and back to the transducer which sends the information to a computer to translate into images. Typically the image is black and white.

Timing of Ultrasounds

Ultrasounds are only given when medically necessary. Although there are currently no rules that regulate the timing and frequency of sonograms, one is usually performed right after the doctor confirms the pregnancy. If it is really early in the pregnancy, a transvaginal ultrasound may be performed to check for molar or ectopic pregnancies. Your healthcare provider may order more ultrasounds if he or she suspects there is a problem.

Possible Pregnancy Complications

The primary purpose of sonograms is to confirm the pregnancy and detect fetal abnormalities. Other tests, such as amniocentesis or chorionic villus sampling, may be ordered in addition to the ultrasound exam to assist in diagnosing medical conditions. Here is a list of possible reasons your doctor may order a sonogram based on trimester:

First Trimester:

  • Confirm pregnancy is viable
  • Ensure baby’s heart is beating
  • Measure gestational age
  • Check for molar or ectopic pregnancies
  • Determine if gestation is normal or abnormal

Second Trimester:

  • Diagnose fetal abnormalities
    • Down syndrome may be diagnosed at 13-14 weeks
    • Congenital malformations may be diagnosed at 18-20 weeks
  • Structural abnormalities
  • Confirm number of fetuses present
  • Verify conception dates and monitor fetal growth
  • Confirm fetal death
  • Identify excessive (hydramnios) or reduced levels (oligohydramnios) of amniotic fluid

Third Trimester:

  • Determine location of placenta
  • Confirm fetal death
  • See how the baby is positioned
  • Monitor fetal movements
  • Identify abnormalities of the uterus or pelvis
Are Sonograms Safe for Mother and Baby?

Ultrasounds are non-invasive and have not been shown to cause harm to babies or mothers. However, the effects of long-term or repeated exposure to ultrasound waves on babies are unknown.

Frequently Asked Questions

Is there a problem if a heartbeat is not detected at 6 to 7 weeks?

There are a few reasons why a fetal heartbeat may not be detected including large abdomen, tipped uterus, or the fetus is younger than previously determined. However, your healthcare provider may be concerned if the fetus has a crown to rump length that is larger than 5mm and there is no heartbeat. A transvaginal probe is typically used for listening to the fetal heartbeat so early in the pregnancy.

Can fetal age be accurately determined using an ultrasound?

A healthcare provider will use a variety of methods to determine fetal age including ultrasounds. However, variations in menstrual cycles and rate of fetal growth make it difficult to accurately assess gestational age. The original estimated fetal age will not change if your doctor uses an ultrasound exam to determine delivery date and assess prenatal care needs.

Why is there such a variation in sonogram scheduling between healthcare providers?

Sonograms are typically conducted only when there is a medical need and individual healthcare providers may define this differently. Typically, they will perform a sonogram if there is a question about the location of the placenta, fetal age, or if complications arise. The majority of pregnancies do not require an ultrasound.

Can sonograms help determine paternity by accurately predicting conception date?

In general, the date of conception can only be estimated because of differences in women’s menstrual cycles and the viability of sperm. Sperm can live inside the uterus for up to five days after intercourse and conception can occur at anytime during that period. Additionally, dating using ultrasound technology can be off by up to seven days. Your doctor will use a combination of factors such as hormone levels and date of last menstrual cycle to help determine conception and fetal age. If paternity is a concern for you, your doctor can recommend other tests that may assist in determining the baby’s father.

When will I know the sex of my baby?

The baby’s sex can usually be determined around 18 to 20 weeks. Unfortunately, 100% accuracy cannot be assured as the prediction can be complicated by the position of the fetus and gestational age. An ultrasound can reveal if you are having multiple children around this time as well.

Are ultrasounds required?

No. Your healthcare provider will only order a sonogram if there is a medical need for it. Typically, your doctor will order at least one to evaluate fetal health and to watch for potential problems.