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The Nub Theory

Updated: May 8, 2021

Can the nub theory show the sex of my baby?

Can the nub theory accurately predict the sex of my baby? Some parents to be are eager to find out the sex of their unborn baby as soon as possible. If you are/were an expectant mother, you may be familiar with old wives tales. These are researched daily in early pregnancy, but are all in good fun, as these are not shown to be accurate. At your 12 week scan you may be introduced to the nub theory. The nub theory is the most research method for predicting your baby's sex as early as 12 weeks. Still today there is a huge debate as to whether this theory is even reliable? Backed by science with studies trialed and tested, the nub theory is up to 99.9% accurate, as long as you have a clear scan of your baby taken at a mid sagital plane, your baby is at a gestation of 12 weeks 5 days and above, and making sure his or her nub is imaging clearly.

So How does it work?

All babies start off with a genital tubercle, or what we have come to know as a "Nub". This nub is compromised of dense tissue that will develop into your baby's genitalia. The nub can be viewed via ultrasound in a mid sagital plane. If the tubercle is pointing at a caudal angle (downward towards the rump) and less than 30 degrees to the axis of the dorsal surface (baby's back/ spine), that indicates female. If the tubercle is at a cranial angle (upwards towards the cranium) and at an angle greater than 30 degrees to the axis of the dorsal surface, this indicates male. All nubs image as a fork. This fork is split into two parts.The bottom half also known as the urogenital folds will develop into the labia minora, and the top half will develop into the clitoris and will continue to retract into its final resting place in the weeks to come. The sex of your baby is chosen from the moment of conception.

Bladder can be used as an anchor to measure this angle.

What the experts say

Before 10 weeks of pregnancy, the genital tubercle appears to be the same in both male and female fetus’s Between 12-14 weeks there is a substantial difference in how the nub appears and so predicting at this gestation is up to 99.9% accurate. After 14 weeks, it is possible for the sonographer to determine gender at your appointment, however most ultrasound technicians will want to wait until at least 16 weeks when the genitals are easily viewed.

How can they tell?

If the angle of the nub is greater than 30 degrees in relation to the spine, you're likely to be having a boy. If it is at an angle of under 30 degrees, straight out or down, you're likely to be having a girl.

How reliable is the theory?

Scientific research shows that the nub theory is very reliable, as long as it is done by someone with experience in the nub theory.

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