The day is finally here: you’re 20 weeks pregnant, and you’re about to find out the sex of your baby. Right after the gender ultrasound, you’re going to run out and buy a tiny blue onesie or a can of pink paint. But then someone bursts your bubble with the news that their friend’s cousin’s neighbor was told she was having a boy, but a girl came out! So just how reliable are these anatomy scans? Can a gender ultrasound be wrong?

For those of you who have never had one, an ultrasound machine uses high-frequency sound waves to make images of organs and structures inside the body. During pregnancy, obstetricians use ultrasounds to monitor the baby’s development and check the mother’s pelvic organs. The twenty-week ultrasound, however, is the “big one.”

So, can a gender ultrasound be wrong?

“At this point in pregnancy, although the fetal organs are still immature, they are all formed, including all the inflow and outflow tracts of the heart — the vena cava, aorta, and pulmonary arteries,” Dr. Bart Putterman, an ob-gyn at Texas Children’s Pavilion for Women in Houston told Parents.com. “The purpose of the 20- to 22-week ultrasound is to look at all of the fetus’s anatomy and to determine if all looks normal. Things that can’t be seen in earlier scans, such as spinal cord abnormalities, brain defects, heart defects, and diaphragmatic abnormalities, can usually be seen on these scans.”

At 20 weeks gestation, a baby’s sex organs should be obvious…assuming the baby cooperates. Sometimes the positioning of the baby makes it impossible for the sex to be determined. When that happens, the tech or doctor won’t venture a guess at all.

But how often are ultrasounds wrong?

Only about 2% of the time! That being said, a doctor or ultrasound tech will usually tell the parents how certain they are with their prediction. The most accurate way to know the sex of a baby is through an amniocentesis or Chorionic Villus Sampling (CVS). However, those tests carry a risk of miscarriage and are only performed when problems are suspected.

So, buy all the pink or blue baby stuff your heart desires! But don’t get rid of the receipts.

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