Skip to main content

What is the nub theory and does it work?

Medically reviewed by Last updated on Nov 6, 2023.

Official answer


Nub theory is an unproven gender prediction method that suggests you can determine your baby's gender at your 12 week pregnancy scan. It centers on the ‘nub’ - the genital tubercle -, that forms on the lower abdomen of the baby. The tubercle or tube will eventually develop into a penis in a male baby or a clitoris in a female baby.

Nub theory states that if the nub is at a certain angle, known as the ‘angle of the dangle’, it can predict the gender of your baby.

  • If the nub points up at a 30 degree angle then its more likely to be a boy
  • If it’s almost flat then it may be a girl.

To be able to have the best chance of seeing the nub clearly in an ultrasound you will need your baby lying nice and flat on their side and not curled up.

Remember, readings can be wrong though so it's best to wait till your 20 week scan to have a clearer picture of your baby's gender on the scan. Alternatively, a noninvasive prenatal test (NIPT), which is a blood test used to screen for genetic abnormalities, can nowadays be used to reveal the gender of the baby during the first trimester.

Nub theory is essentially just a theory as there is no scientific evidence to back up this method. Up until the 14th or 15th week of pregnancy, a baby's genitalia is very similar looking on scans between males and females and to make a prediction at this early developmental stage can produce inaccurate results.

From 17 weeks onwards is when a baby’s genitalia is more defined and your healthcare professional may be able to determine gender more accurately during a scan. The most important thing to concentrate on is the health of your baby.