How Accurate Are Gender Ultrasounds?

Learn more about the accuracy of gender ultrasounds during pregnancy and how health care providers determine fetal sex. 

Ultrasounds are a key tool for monitoring the health of your fetus, but they can also serve another exciting purpose for some parents: Revealing their sex. But how do ultrasounds work to predict gender, and are they always accurate? We spoke with experts to break down your most pressing questions.

While this article uses the terms "gender" and "boy" vs. "girl," it's important to note that gender is a personal identity that exists on a spectrum, can change over the course of a person's lifetime—and most importantly—is something that a person defines for themselves. Sex, on the other hand, is assigned at birth based on the appearance of a baby's genitalia. While sex assigned at birth often matches a person's gender (called cisgender), sometimes, for transgender, intersex, and gender nonbinary people, it does not.

What Is a Gender Ultrasound?

Health care providers do not perform ultrasounds during pregnancy solely to determine your baby's sex. Instead, technicians often observe your baby's genitalia during a routine anatomy scan, which takes place in the second trimester, usually between 18 and 22 weeks.

While some people wait until their baby is born to find out if they're having a boy or a girl, others want to know as soon as possible. Ultrasounds are a non-invasive way to get a good guess during pregnancy.

These ultrasounds, though commonly referred to as "gender ultrasounds," are actually anatomy scans that evaluate how your baby is developing. It just also happens that since technicians are so frequently asked about a baby's sex, they also look for visible external genitalia to satisfy parents' curiosity.

What Happens During the Ultrasound

While you're reclining on an exam table, the ultrasound technician will slather gel on your belly. Then, they'll glide over it with a plastic transducer that emits high-frequency sound waves. These waves bounce off your little one's body to produce an image of their soft tissues and organs.

According to Penn Medicine, during an anatomy scan, a health care provider will evaluate the fetus from head to toe, including a detailed look at:

  • Their estimated weight and length
  • Their face, paying particular attention to lips and palate
  • Their brain
  • Their spine
  • Their heart
  • Their kidneys
  • Their limbs

In addition, a technician will assess the health of the placenta. Technicians will often also attempt to view your baby's genitalia since many parents want to know the sex. The image will be displayed on a monitor for you (and anyone you may have with you) to see.

According to the Food and Drug Administration (FDA), ultrasounds are considered safe when done by a trained technician for medical purposes, and they don't involve X-rays or radiation. The exam also doesn't hurt, although the gel may feel a bit cold and messy.

pink and blue shoes and ultrasound
Getty Images

Accuracy of Boy vs. Girl Ultrasound Predictions

As it turns out, ultrasounds are pretty accurate for identifying whether a fetus has a penis or a vulva, particularly in the second and third trimesters. A 2015 study found that ultrasound technicians correctly predict a baby's assigned sex nearly 100% of the time after 14 weeks gestation. Estimates regarding a fetus' sex based on ultrasound during the first trimester (between 11 and 14 weeks in the study) are less accurate with ultrasound technicians being right about 75% of the time.

Typically, you can expect an ultrasound between 18 and 22 weeks during which the technician is likely to share their findings unless you explicitly ask them not to. Still, the accuracy of your exam results will depend on several factors, including timing, your baby's position, your body size, and whether you're carrying multiples.

Timing

How far along the pregnancy is makes a big difference in the accuracy of so-called gender ultrasounds. "The accuracy of the ultrasounds increases as gestational age advances," says Bart Putterman, M.D., an OB-GYN at Texas Children's Pavilion for Women in Houston. Waiting until the second trimester increases the likelihood of getting an accurate reading because the fetus' genitals are more developed and easier to see.

Your baby's position

If your sonographer is having a tough time seeing between your baby's legs because of their position, it will impair their ability to determine your baby's sex. "If they are not clearly visualized, mistakes can be made when sonographers guess the gender based on a suboptimal examination," says Dr. Putterman.

Your body size

If you have a larger body, determining a fetus' sex on ultrasound is more difficult, says Michele Hakakha, M.D., a Beverly Hills-based OB-GYN and the author of Expecting 411: An Insiders Guide to Pregnancy and Childbirth. However, an experienced ultrasound operator should be able to get a clear picture for people of all sizes.

Pregnancy with multiples

If you're carrying twins or triplets (or more!), your babies could hide their siblings, making the determination of the sex of each baby more difficult.

When Should I Get a Gender Ultrasound?

Early ultrasounds aren't the most accurate gauge of whether you're expecting a boy or girl. "The earliest in pregnancy that the fetus's sex can be determined by ultrasound is about 12 weeks, and even then, it can be very difficult," says Dr. Hakakha. "The external genitalia—the vulva or penis and scrotum—are not actually external until about 13 weeks."

You may want to wait until later ultrasounds, such as your 20-week anatomy scan, for a more definitive answer.

The Bottom Line

It's exciting to learn your baby's sex, but keep in mind that these predictions are sometimes inaccurate or incomplete. In some cases, technicians make an error. And in other cases, your child's gender (their internal sense of who they are) may not match the sex they were assigned at birth. So, either way, it's best to keep an open mind.

Additional reporting by
Nicole Harris
Nicole Harris, SEO Editor
Nicole Harris is the Editor at Parents. She joined the team in 2018 as a Staff Writer and was promoted to SEO Editor in 2021. She now covers everything from children's health to parenting trends. Nicole's writing has appeared in Martha Stewart Weddings, Good Housekeeping, The Knot, BobVila.com, and other publications. A graduate of Syracuse University, Nicole currently lives in New Jersey with her husband.
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