Nub Theory

Using this method is highly accurate. When your baby’s nub (genital tubercle) is forming and visible around 12 weeks, the angle of the dangle can assist in predicting the sex of your baby.

What is a nub?

Before about 15 week gestation, both males and females have genital tubercles, also known as a nub. This is basically a small part of your baby’s anatomy that will eventually develop into their gender-specific genitals.   Determining gender is now possible between 12-14 weeks gestation by analyzing the angle and shape of the nub, also referred to as the “angle of the dangle.” The scan must be in profile view in order to allow viewing of the spine and the nub’s relationship to it. This angle is directly related to whether the child will be a boy or a girl.  

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 in the next example scan, there is a “shadow” on the tip of the baby’s nub. That shadow can be an indicator that the nub will soon develop the distinctly penis-like features that mark a boy. 

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.


Select a Product and upload your scan. Our experts will review and deliver The Gender Prediction Report same day, directly to your E-mail.


How do The Gender Experts Predict Nub Theory? After submitting your 12-14 week ultrasound scan, rather than waiting for your 20 week Anatomy 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 
  • The 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 

These factors contribute to the nub theory being scientifically proven and provides an impressively accurate prediction of your baby’s gender. 

How early can I use the Nub Theory to know whether it will be a boy or girl?

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?

Nub Theory accuracy ranges from 80-92%. Such a wide range of accuracy is based on factors such as the visibility of the nub, the angle of the fetus, abdominal wall thickness, and the amount of amniotic fluid. More amniotic fluid = greater visibility of the fetus at your ultrasound, so make sure to drink plenty of water in the week leading up to your ultrasound. For a better fetal angle in the photo, make sure you drink some juice or have a healthy snack before you go to your ultrasound – the food will help the baby move around more, so you get more visible angles. 


Having one of our technicians analyze your scan will help differentiate between the actual nub and what may be the umbilical cord, leg/femur, foot and other parts of the baby’s body that may look like the nub.

If your baby’s nub is not visible or the baby is in a less than optimal position, we will let you know. We will give you the option to try a Skull Theory prediction or offer a full refund.

Accuracy rates increase with greater visibility, when scanning in person, and when combined with a Ramzi Theory scan. 

Nub Theory vs. Gender Calendars and Gender Charts

If you’ve been looking into finding out the gender of your baby as early as possible, and don’t want to rely on old wives tales, you’ve probably come across one or many of the different ‘methods’ listed online in forums and other places. These include ancient tactics like our original Chinese birth calendar, and Indian Gender prediction test, among other methods.

Unfortunately, even the most accurate Chinese gender prediction chart doesn’t do much better than giving you a 50-50 chance of guessing the gender accurately. Nub theory, on the other hand, provides an accurate gender prediction in roughly 9 out of 10 cases.


So even if you’re still wondering, “What’s a nub in the first place?” Our experts know everything necessary to use your early ultrasound to provide you with an accurate, customized prediction of your baby’s gender. Please feel free to contact us directly if you’d like to learn more about this process, or just want to ask — “Where is a nub on scan sheets from our ultrasound?”

We’re here to answer your questions and provide the earliest, most accurate baby gender predictions available anywhere.

Submit Your Ultrasound Scan for a Nub Theory Gender Prediction