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Nub Theory and predicting your baby’s gender from an Ultrasound

February 11, 2021

Have you hear of the Nub Theory?

The Nub Theory is a theory for predicting the gender of your baby very early on in your pregnancy using an ultrasound image.

Before 14 weeks of gestation, both male and female fetuses have an anatomical body part between the legs called a genital tubercle, otherwise known as “the nub.” This genital tubercle, or nub, is what develops into the penis in male babies or the clitoris in female babies.

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Predicting you baby’s gender with a first trimester Ultrasound

According to the Nub Theory, specific ultrasound measurements taken between 12 and 14 weeks of pregnancy can be used to calculate the angle of the genital tubercle in relation to the fetal spine, which can determine whether the fetus is a boy or a girl. In other words, the “angle of the dangle” can tell you if that nub will go on to develop into a penis or clitoris.

There are even gender prediction services online where you upload photo of your first trimester Ultrasound and for a small fee, they predict your baby’s gender. Check out The Gender Experts (no affiliation, just fascination).

nub theory girl gender prediction

Image credit: The Gender Experts

nub theory boy gender prediction

The science behind the Nub Theory

While it might be a theory, scientific papers have been written on the subject and the results suggest the theory is very accurate when predicted by a trained eye between 12-14 week ultrasound.

Scientific studies have been performed on gender prediction. Studies like this one:

Fetal gender assignment by first‐trimester ultrasound

By Z. EFRAT, T. PERRI, E. RAMATI, D. TUGENDREICH and I. MEIZNER of Department of Obstetrics and Gynecology, Rabin Medical Center, Petah Tikva, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel

Extract of study findings

Gender assignment was possible in 613 of the 656 (93%) fetuses. Gender identification was feasible in 85%, 96% and 97% of the fetuses at gestational ages of 12 to 12 + 3, 12 + 4 to 12 + 6 and 13 to 13 + 6 weeks, respectively. The accuracy of male gender assignment in this group was 99–100% at all ages, and that of female gender assignment was 91.5% at 12 to 12 + 3 weeks, 99% at 12 + 4 to 12 + 6 weeks and 100% at 13 to 13 + 6 weeks.

Extract of Conclusion

Prenatal gender assignment by ultrasound has a high accuracy rate at 12–14 weeks.

While it might be a theory, scientific papers have been written on the subject and the results suggest the theory is very accurate when predicted by a trained eye between 12-14 week ultrasound.

More about this paper

While it might be a theory, scientific papers have been written on the subject and the results suggest the theory is very accurate when predicted by a trained eye between 12-14 week ultrasound.

nub theory ultrasound technician with pregnant lady

We’d love to hear whether or not your Nub Theory guesses were accurate! Share your story with us on Instagram @hello.bebebola
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