As it turns out, most women only need a couple of ultrasounds during pregnancy. Read on to learn more about these important prenatal exams.

By Tricia O'Brien and Nicole Harris
Updated December 15, 2019

Pregnancy ultrasounds provide your doctor with plenty of valuable information. The results allow him to monitor your baby's growth, detect abnormalities, predict your due date, determine whether you're carrying multiples, see the position of your placenta, and make out the sex of your baby. But how many ultrasounds are safe during pregnancy, and when should you schedule the exams? We have the information you need to know.

What Are Ultrasounds?

During an ultrasound, your doctor or a skilled technician uses a plastic transducer to transmit high-frequency sound waves through your uterus. These sound waves send signals back to a machine that converts them into images of your baby. 

The test doesn't hurt, although gel (used to guide the transducer on the stomach) may feel cold and be messy. You should wear two-piece clothing to allow easy access to your tummy. 

Note that it will be hard to see much during the first few weeks of pregnancy, but a clearer photo will come around 13 weeks, which is the ideal time to share your exciting news.

How Many Ultrasounds Do You Get During Pregnancy?

Wondering how many times you’ll need to undergo an ultrasound? This varies based on the woman and her pregnancy. Here are some ultrasound exams you might have while expecting. 

Early Pregnancy Ultrasound (6-8 Weeks)

Your first ultrasound, also known as a sonogram, may take place when you're around 6 to 8 weeks pregnant. However, some doctors only conduct this exam if you have certain high-risk pregnancy conditions. These include bleeding, abdominal pain, and history of birth defects or miscarriage

This first exam may be conducted transgvaginally so doctors get a clearer picture of your baby. In this case, you OB-GYN will place a thin wand-like transducer probe—which transmits high-frequency sound waves through your uterus—in your vagina. The sound waves bounce off the fetus and send signals back to a machine that converts these reflections into a black and white image of your baby.  

At 6 weeks' gestation, it's possible to see the baby's heartbeat. Your practitioner will also predict your baby’s due date, track milestones, determine the number of babies in the womb, and see whether you have an ectopic pregnancy.  

Dating Ultrasound (10-13 Weeks)

Those who forgo the 6-8 week ultrasound might have  a”dating ultrasound” around weeks 10-13. This gives parents the same type of information: due date, your baby’s “crown-rump length” (measurement from head to bottom), the number of babies in the womb, and fetal heartbeat

Nuchal Translucency Ultrasound (14-20 Weeks)

Between 14 and 20 weeks, you may also have a nuchal translucency (NT) test to check for Down syndrome and other chromosomal abnormalities, says Joanne Stone, M.D., a professor of obstetrics, gynecology, and reproductive Science at Mount Sinai School of Medicine in New York. Women whose screening test revealed a potential problem, who are 35 or older, or who have a family history of certain birth defects should consider it.  Doctors will measure hormones and proteins with a blood test, and they'll also gauge the thickness at the back of the baby's neck with an ultrasound. A thicker neck may indicate an increased risk for birth defects like Down syndrome and trisomy 18.

Anatomical Survey (18-20 Weeks)

This detailed ultrasound, generally between weeks 18 to 20 of pregnancy, lasts 20 to 45 minutes if you're having one baby and longer if you're having multiples. This is the most thorough checkup your baby will have before she is born. 

The doctor will check your baby's heart rate and look for abnormalities in her brain, heart, kidneys, and liver, says Jane Chueh, M.D., director of prenatal diagnosis and therapy at Lucile Children's Hospital Stanford, in Palo Alto, California. She'll count your baby's fingers and toes, check for birth defects, examine the placenta, and measure the amniotic fluid level. And she'll probably be able to determine your baby’s sex, although it's not a slam dunk; an experienced tech gets it right more than 95 percent of the time. (If you don't want to know your baby's sex, let her know ahead of time.) 

Third Trimester Ultrasounds

Many moms-to-be don't need an ultrasound in the third trimester. But if your pregnancy is considered high-risk—for example, if you have high blood pressure, bleeding, low levels of amniotic fluid, preterm contractions, or are over age 35 —your doctor may perform in-office, low-resolution ultrasounds during your prenatal visits for reassurance, says Dr. Chueh. You'll also get a follow-up scan if your cervix was covered by the placenta at your 20-week scan.

Doppler Fetal Monitoring

This test is typically performed during the last trimester on women who suffer from gestational diabetes. A regular ultrasound uses sound waves to produce images; this one bounces high-frequency sound waves off circulating red blood cells to measure blood flow and blood pressure. The test will determine if Baby is getting enough blood.

How Many Ultrasounds Are Safe?

An ultrasound is considered safe for both you and your baby when it's used for medical purposes. Although ultrasounds require no radition, only a trained professional who can interpret the results with accuracy should perform them. Your technician should be schooled in obstetrical ultrasound, preferably at a center accredited by the American Institute of Ultrasound in Medicine

Some medical practices now offer 3D (high quality and lifelike) and 4D (moving picture) ultrasounds, which may help doctors detect certain fetal abnormalities and birth defects. However, these types of exams are also available at fetal portrait studios in places like shopping malls. Experts discourage these “keepsake” ultrasounds since untrained personnel may give out inaccurate information, says Michele Hakakha, M.D., an OB-GYN in Beverly Hills and author of Expecting 411.

Plus, although ultrasounds are safe in medical settings, they might heat tissues or produce bubbles (cavitation) during use. Experts aren’t sure about the long-term effects of heated tissues or cavitation when ultrasounds are conducted outside of a medical need with non-trained professionals. “Therefore, ultrasound scans should be done only when there is a medical need, based on a prescription, and performed by appropriately-trained operators,” according to the FDA in a December 2014 statement

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