Why Sonograms Get a Baby's Sex Wrong Sometimes

You can’t always depend on a sonogram to learn a baby’s sex. (Photo: Getty Images)

At a sonogram appointment 13 weeks into her third pregnancy, Alison Busca, 39 and then living in Rome, was told that her unborn child was a boy. “I already had an older boy and a girl, so I wasn’t hoping for one sex or the other,” Busca tells Yahoo Parenting. However, three weeks later, during another sonogram appointment, both her doctor and a nurse had surprising news: Busca was actually having a girl.

The doctor didn’t have much explanation for why the sex of her baby had suddenly changed, says Busca, so she chalked it up to a simple misread.

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But at the end of the summer, around 23 weeks into her pregnancy, Busca’s first 3D ultrasound revealed that the baby was, in fact, a boy. “My husband and I were shocked, but we were able to laugh it off, joking about the girl clothes we’d received [as gifts] and reconsidered baby names,” she says.

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While it’s tough to know how often sonograms yield false sex results, there are two possible explanations: Sex organs are extremely small before 20 weeks, making it difficult for doctors to view them, and babies can contort themselves into positions that don’t always offer a clear understanding of their sex.

And while most doctors stress that the goal of a sonogram is to assess the health and development of a fetus — not to determine sex — there are techniques to obtain a more accurate reading.

Be patient. “Early exams can have inaccuracies relating to the baby’s sex,” sonographer Pamala Thacker tells Yahoo Parenting. “At 20 weeks, I can usually tell with certainty whether it’s a girl or a boy.” She also advises against 3D ultrasounds conducted at nonmedical facilities, such as in malls and private offices. These types of exams, often performed too early and not usually by medical professionals, can give false results.

Don’t jump to conclusions. “Sonographers may call the sex even when they’re not certain,” says Thacker, who attributes such misinformation to the pressure to please eager patients. Other times, excitement can cause people to misinterpret the results. For example, Thacker worked with a sonographer who told a patient that the sex of her baby was unclear. Despite the tech’s uncertainty, the expecting mom assumed she was having a girl and was upset when she eventually discovered she was having a boy.

Eat before the appointment. Giving your baby some fuel before a sonogram will help him or her have the energy to move around and show the camera a variety of angles. But don’t overeat. Thacker recalls one patient who was worried about the baby being too still, so she drank five Mountain Dews before the sonogram. “That kid acted so crazy it made the exam more difficult to perform.”

Wait to go to the bathroom. “It’s best to have a full bladder,” Jacob Avila, a Chattanooga, Tenn.-based ultrasound technician, tells Yahoo Parenting. If it’s an emergency, go, but a full, cushy bladder can help a baby move into position.

Remember what the ultrasound is really for. While no one can blame couples for wanting to know the sex of their unborn baby, that’s not Thacker’s or any tech’s priority. “We want to make sure your baby is alive and healthy and growing normally,” she says. “When something is wrong, we act calm, speak to the doctor, and get you taken care of, but trust me, our hearts are broken. These tests aren’t done to determine sex.”

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