How to Tell a Baby’s Gender on an Ultrasound

Most new parents decide to find out their baby’s gender before birth. A study by Obstetrics and Gynecology found that 69% of parents wanted to know. The reasons given varied from “out of curiosity”, “because it was possible”, and they “just wanted to know”.

An ultrasound is the best tool available to reveal the gender in utero. It’s a noninvasive technology that uses sound waves to create images. Viewing fetuses during prenatal care is the most common use for the ultrasound technology. When used in this way, it’s called obstetric sonography. Between 18 to 20 of weeks of pregnancy, a detailed scan can be performed, called a level 2 ultrasound. The sonographer will measure the size of the baby, check the major organs, check the placenta, and measure the amniotic fluid level to make sure everything is developing as it should be. During a level 2 exam, the sex of the baby can also be seen with a high degree of certainty.

How to Tell a Baby’s Gender on an Ultrasound

When determining a baby’s sex, the absence of a penis doesn’t necessarily mean it’s a girl. Excessive movement by the baby during the exam can send back bad images that make it difficult to see what the sex is. Under optimal conditions though, using an ultrasound to find the sex has been proven 100% accurate in some studies. The variables that can lead to mistakes are the sonographer’s experience, fetal age, and fetal sex.

Signs of a Girl

When determining the sex of the fetus, the technician will look for certain characteristics unique to both sexes. In girls, they look for the “hamburger sign” of three white lines during the ultrasound. The three lines show the labia on the sides and the clitoris in the middle. The sagittal sign involves taking a profile of the fetus on the sagittal plane. On the image, follow the baby’s spine to the tailbone with a nub at the end of it. If it’s a girl, there will be a downward pointing notch on the nub.

Signs of a Boy

If the baby is a boy, the sagittal sign can still be used. The difference is that the notch will face upward. The flow of urine from the baby can sometimes be seen, and if it’s moving upward, it’s more likely a boy—this is more difficult to see than other signs, though. Male genitalia are easier to see on ultrasound when the baby isn’t moving, so if a penis, scrotum, and testicles can be seen, that is indisputable proof it’s a boy.

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How to Tell a Baby’s Gender on an Ultrasound