How Is an Ultrasound Used During Pregnancy?

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Ultrasound—also known as a sonogram—is a medical imaging technique that uses sound waves to see inside the body. In pregnancy, ultrasound is used to scan the abdomen and pelvic cavity to view the fetus and placenta. Ultrasounds may be performed at any stage during pregnancy.

Ultrasound during pregnancy

 Jose Luis Pelaez Inc / Getty Images

Purpose

Ultrasound allows medical professionals to monitor the health and development of the fetus. It can also be used to elevate health conditions of the mother. There may be different reasons to perform an ultrasound based on the different stages of pregnancy.

First Trimester

  • Confirm pregnancy is viable
  • Confirm heartbeat
  • Evaluate for ectopic pregnancy—when a fertilized ovum implants outside of the uterus
  • Evaluate for molar pregnancy—a type of gestational trophoblastic disease
  • Determine gestational age
  • Confirm multiples pregnancy
  • Identify pelvic or uterine abnormalities in mother

Second Trimester

  • Diagnose fetal malformation
  • Look for characteristics of Down syndrome
  • Confirm the baby is growing normally
  • Identify location of placenta

Third Trimester

  • Observe if the fetus is moving as it should
  • View location of placenta if discovered to be in an abnormal position during an earlier ultrasound
  • Confirm the baby is growing normally

Types

There are three forms of prenatal ultrasound: standard, limited, and specialized.

Standard

A standard ultrasound is used to check the physical development of the fetus, as well as to estimate the gestational age and screen for major congenital malformations.

A standard ultrasound can also be used to determine:

  • Number of fetuses
  • Estimated size and weight of fetus
  • Position of fetus
  • Heart rate and breathing of fetus
  • Location of placenta

In some instances, it may be possible to determine the sex of the fetus in a standard ultrasound. This depends on the position of the fetus.

Limited

A limited ultrasound is performed to answer specific questions. This can be used:

  • If there is vaginal bleeding during pregnancy, to see if the placenta is too low
  • In labor to see where the fetus is positioned in the uterus
  • At any point to see if the fetus’s heart has stopped beating

Specialized

A specialized ultrasound is performed if a problem is suspected. This may be based on risk factors or results from other tests. Depending on the problem suspected, techniques like Doppler ultrasonography or 3D ultrasonography may be used.

Transvaginal vs. Transabdominal

In pregnancy, there are two types of ultrasounds:

  • Transvaginal: The ultrasound probe is inserted into the vagina.
  • Transabdominal: The test is performed externally, placing the ultrasound transducer on the abdomen and down to the pelvic area.

The type of ultrasound you have will depend on why the exam is being performed.

Transvaginal Ultrasound

During a transvaginal ultrasound, you will:

  1. Be asked to either change into a hospital gown, or undress from the waist down
  2. Lie on your back and be asked either to bend your knees or have your feet in stirrups
  3. Have an ultrasound probe, also called a transducer, inserted by the healthcare provider into your vagina: The probe is covered in a condom-like latex sheath and will be lubricated.
  4. Perhaps experience some discomfort as the probe is being inserted, but it shouldn’t hurt
  5. Feel the probe gently moving around to view the uterus and fetus: You may feel some pressure when this occurs.
  6. Perhaps hear a “whoosh whoosh” noise
  7. See images on the ultrasound machine

The test will take approximately 30 to 60 minutes.

Transabdominal Ultrasound

During a transabdominal ultrasound, you will:

  1. Be asked to remove clothing from the waist up: You may be asked to change into a gown.
  2. Lie on your back and a gel will be applied to your abdomen
  3. Feel the ultrasound technician or healthcare provider press the ultrasound transducer against the skin of your abdomen: They will move the transducer across your abdomen. This shouldn’t hurt.
  4. Perhaps hear a sound like “whoosh whoosh” when it is in use
  5. See images displayed on the ultrasound machine screen: In many cases you will be able to see these images as the ultrasound is being performed.

At the end of the procedure, the gel will be removed from your abdomen. The test will take approximately 30 to 60 minutes.

Frequency

The number of ultrasounds required during pregnancy varies from person to person. How many you need will be determined by your healthcare provider and may be based on:

  • Risk factors
  • Development of the fetus
  • Your health as the mother

The American College of Obstetricians and Gynecologists advises there should be at least one standard ultrasound during pregnancy, typically performed at 18-22 weeks.

When ultrasounds are performed during the first trimester, the healthcare professional usually checks:

  • If the fetus is viable
  • The number of fetuses
  • If the pregnancy is outside of the uterus

Safety

Ultrasound has been used for more than 20 years and doesn’t have the same risks as X-rays or other imaging exams that use ionizing radiation.

No radiation is used during ultrasound.

Low Risk

There is no evidence to suggest ultrasound is harmful for the fetus. There have been no links between ultrasound and:

  • Childhood cancer
  • Birth defects
  • Developmental problems for the fetus later in life

Even though safe, the American College of Obstetricians and Gynecologists advises that ultrasound should only be performed for medical reasons, with casual use being avoided.

Use of ultrasound in pregnancy for non-medical reasons (like for the purpose of “keepsake” images or videos) is not recommended. These “keepsakes” can be obtained during ultrasound exams that are medically indicated if no additional exposure is required.

Although considered generally safe when undertaken by a trained medical professional, there are potential impacts on the body from an ultrasound, including the possibility that:

  • Ultrasound waves may heat tissues
  • Small pockets of gas could form in body fluids or tissues

The long-term impacts of these are unknown.

Transvaginal ultrasound may cause some discomfort. Those with a latex allergy may react to the latex sheath used to cover the ultrasound probe during a transvaginal ultrasound.

A Word From Verywell

Ultrasound is an imaging tool that medical professionals may use throughout pregnancy to monitor the health and development of the fetus, as well as the health of the mother. It is a safe procedure that may need to be performed at any stage of pregnancy. If you have concerns about ultrasound during your pregnancy, speak with your healthcare provider.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Pregnancy Association. Ultrasound: sonogram. Updated April 25, 2020.

  2. American College of Obstetrics and Gynecologists. Ultrasound exams. Updated June 2020.

  3. Johns Hopkins Medicine. Pelvic ultrasound.

  4. MedlinePlus. Transvaginal ultrasound.

  5. Food and Drug Administration. Ultrasound imaging. Updated September 28, 2020.