1st trimester ultrasound

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First trimester ultrasound

In the first trimester, an early ultrasound is often a routine part of prenatal care between 6 to 9 weeks of pregnancy. However a first-trimester ultrasound isn’t standard practice, because it’s still too early for your practitioner to see your baby in detail.

Most practitioners wait until at least 6 weeks to perform a first pregnancy ultrasound. However, a gestational sac can be seen as early as 4 1/2 weeks after your last period, and a fetal heartbeat can be detected at 5 to 6 weeks (though it might not always be).

If your doctor does decide to perform a first-trimester ultrasound, it gives you a welcome first glance of your baby. This sneak peak is used to:

  • Confirm your estimated due date more accurately by measuring the fetus
  • Check the fetal heartbeat
  • Make sure the pregnancy is in the uterus (to rule out an ectopic pregnancy)
  • Determine the number of fetuses

Hearing a Fetal Heartbeat

Second trimester ultrasound

Midway through your pregnancy, between week 18 and week 22, a detailed anatomy scan called a level 2 ultrasound is performed by a trained sonographer.

The second trimester ultrasound is reassuring and fun to watch. It also offers you and your practitioner a picture of the overall health of your baby and your pregnancy by:

  • Measuring your baby’s size and checking all major organs
  • Estimating the amount of amniotic fluid in your uterus, to make sure the level’s as expected
  • Verifying the position of the placenta
  • Telling you your baby’s sex (if you want to know)
  • Giving you a sneak peek at your baby (ask the sonographer to point out your baby’s hands, feet and face!)

Routine second trimester ultrasounds are usually done in 2D. Most practitioners reserve the more detailed 3D and 4D ultrasounds for when they’re medically necessary, to more closely examine a fetus for a suspected anomaly. While ultrasound technology is considered very safe, practitioners prefer to be extra cautious and minimize intrusions into your womb.

Additional ultrasounds during pregnancy

There are several reasons you may have additional ultrasounds during your pregnancy, including if:

  • You have any spotting during pregnancy, to confirm that all is well
  • You’re carrying multiples, to monitor their growth
  • You’re at risk of preterm labor, to check for changes in the cervix
  • Your practitioner wants to check toward the end of pregnancy whether your baby may be too large to deliver vaginally (for example, you have a very small pelvis or your practitioner suspects your baby is very large due to gestational diabetes)
  • Your practitioner wants to verify if your baby’s in a heads-down position before birth

Additionally, ultrasounds are a part of several other tests, including:

  • Chorionic villus sampling (CVS)
  • Amniocentesis
  • Nuchal translucency screening
  • Biophysical profiles

Doctors sometimes recommend a fetal echocardiogram, or a detailed ultrasound of a baby’s heart that’s performed by a trained technician and analyzed by a pediatric cardiologist. Your practitioner may recommend an echocardiography if you have certain risk factors, including if:

  • You have a family history of congenital heart defects
  • Your baby’s been diagnosed with a genetic abnormality (like Down’s syndrome)
  • You had abnormal results during another pregnancy test
  • You have certain health conditions (like diabetes or an autoimmune disease)
  • Your baby has an abnormal heart rhythm or rate
  • You had certain infections during pregnancy, including rubella or CMV

How to prepare for pregnancy ultrasound

Wondering how to prepare for a pregnancy ultrasound? If you’re getting a transabdominal ultrasound, you should arrive at your appointment with a full bladder. This makes it easier for your doctor to see around or through your bladder.

To time it right, some practitioners suggest emptying your bladder about 90 minutes before your exam. Then drink an 8-ounce beverage of your choice (water, juice and milk are all fine) about an hour before your appointment.

Otherwise, there’s no other specific preparations required for a pregnancy ultrasound, and you can eat normally that day. Your job: sit back and enjoy the show.

What to expect during first pregnancy ultrasound

There are two main types of ultrasounds used during pregnancy: transvaginal and transabdominal ultrasounds. Both types of scans typically last about 20 minutes and are painless. The type of first ultrasound you’ll get depends how far along you are in your pregnancy.

During your first ultrasound, you’ll be able to watch along with your practitioner (though you’ll likely need help to understand what you’re seeing). You’ll likely even take home a small printout as a souvenir.

Transvaginal ultrasound

If you’re getting your first pregnancy ultrasound before week 6 or 7, your practitioner will likely perform a transvaginal ultrasound. A small, long transducer (or wand) is wrapped in a sterile condom-like cover and inserted into the vagina.

The practitioner will then move the wand within the vaginal cavity to scan your uterus. You’ll feel pressure, but it should be painless.

The transducer emits sound waves, which bounce off of structures (otherwise known as your baby) to produce an image you can see on a computer or video screen.

Transabdominal ultrasound

If your first ultrasound is after week 6 to 7, you’ll get a transabdominal ultrasound examination. Gel is rubbed onto your belly to help the sound waves move more easily. Then the wand is rubbed over your belly to produce images of your baby.

This exam shouldn’t hurt, although it can be somewhat uncomfortable if the sonographer needs to press hard on your abdomen to see a particular part of your baby more clearly (especially with a full bladder).

The difference between sonogram and ultrasound

Though the words sonogram and ultrasound are often used interchangeably, there is a distinction:

  • Ultrasound is the term for an imaging test that uses sound to produce pictures.
  • Sonogram is the picture produced by ultrasound technology.

Risks of ultrasounds during pregnancy

Ultrasounds are noninvasive and very low-risk when performed by your healthcare practitioner. There is no rule on how many ultrasounds are safe during pregnancy, but ACOG recommends sticking to just one to two ultrasounds in total (outside of other circumstances where more are medically necessary).

That said, medical guidelines caution against unnecessary exposure to ultrasound. Because no researcher would willingly put a fetus in harm’s way in the name of science, it’s difficult to study the long-term effects of ultrasound use — which means there is the possibility of unintended consequences with overuse.

What’s more, though ultrasounds are usually relatively accurate at estimating a baby’s size, they can underestimate or overestimate weight, especially if they’re overused, which may occasionally result in unnecessary C-sections or premature deliveries.

That’s why ACOG along with the Food and Drug Administration (FDA) urge practitioners and patients to only use ultrasounds if they’re medically necessary. These groups also recommend that pregnant women avoid keepsake 3-D and 4-D sonograms during pregnancy advertised by private companies along with at-home fetal monitors.

Some research has found that the average number of ultrasounds women are receiving is much higher than recommended— more than five over the course of pregnancy, on average. So if your doctor recommends more than two ultrasounds when you’re expecting, don’t hesitate to ask questions to ensure that the extra ultrasounds are medically required.

From the What to Expect editorial team and Heidi Murkoff, author of What to Expect When You’re Expecting. Health information on this site is based on peer-reviewed medical journals and highly respected health organizations and institutions including ACOG (American College of Obstetricians and Gynecologists), CDC (Centers for Disease Control and Prevention) and AAP (American Academy of Pediatrics), as well as the What to Expect books by Heidi Murkoff.