Nub Theory

Submit Nub Theory Ultrasound Scan

for a Gender Prediction from our Experts

Confirmed Nub Theory Database


Nub Theory

Also referred to as the “angle of the dangle.” Before about 15 week gestation, both males and females have genital tubercles. Determining gender is now possible between 12-14 weeks gestation by analyzing the angle and shape of the nub. The scan must be in profile view, to allow viewing of the spine, and the nub’s relationship to it.





If the nub is angled greater than a 30 degree angle in relation to the spine, it is likely a male fetus. If it is pointing straight out, under 30 degrees, or down, it is likely a female fetus!  In our photo example, we illustrate how a male fetus’ genital tubercle is angling at more than 30 degrees in relation to the spine.

As you may be able to see, there is a “shadow” on the tip of this nub. This is another indicator of a male fetus.

The length and shape of the genital tubercle may sometimes indicate gender, but not always. For example, some say that a “forked” shape at the tip is indicative of a girl fetus, however we do not adopt this, as we have seen just as many “forked” boy nubs as forked girl nubs.

How do The Gender Experts Predict Nub Theory?

After submitting your 12-14 week ultrasound scan, The Gender Experts will check for visibility of the genital tubercle. Visibility may be affected by the position of the baby, the amount of amniotic fluid in the sac, thickness of abdominal wall, scan quality and/or resolution.

To determine gender, The Gender Experts use the following criteria:


  • Visibility
  • Angle of genital tubercle in relation to the spine
  • Shadows and male markers on and surrounding tip of nub
  • Shape, including length according to gestational age

When is the ideal time to predict using the Nub Theory?

Before 10 weeks of pregnancy, the genital tuber appears to be the same in both male and female fetus’. At 11 weeks, if the visibility is in perfect conditions, it may be possible to predict, but accuracy will not be as great as weeks 12-14. After 14 weeks, it may be possible for the sonographer to determine gender at the appointment, however most ultrasound technicians wait until your anatomy scan at around week 20.

How accurate is the Nub Theory?

Some studies have proven over 88% accuracy at 12 weeks when scanning in a controlled setting. The Gender Experts have conducted three study groups, and the Nub Theory accuracy rate has ranged from 80-92% for ideal visibility nub scans. Accuracy rates increase with greater visibility, when scanning in person, and when combined with a Ramzi Theory scan.

Our Research and Data studies are in the process of being published, and we are currently conducting our fourth study group. If you would like to be included in our study group, click the following link for more information: Research and Data Studies

Still unsure? Submit your scan or View Confirmed Nub Theory scans for more info.


Confirmed Nub Theory Database