The Nub Theory Explained

What is The Nub Theory?

The Nub Theory is as much a theory as evolution is a theory, you can't argue a nub, it's the infantile version of the genitals, it's both labioscrotal fold and the dense nerve endings that become the clitoris or the head of the penis.

While there may be times it's guessed inaccurately, this is almost down to a bad image, limited images or an early gestation. *It's only down to the nub 5% of the time*.

If there is a recorded video, at 12+5 weeks or more, it's almost inarguable.

Not only does the 'angle of the dangle' help with predicting your baby's sex but other factors come into account, such as your baby's bladder location, baby's positioning, exact gestation that your baby was measuring on the day of the scan and of course, a clear nub shot.

Developing Nubs

Scientific studies have shown that out of a total 1619 pregnancies, 1424 babies were predicted correctly.

This chart shows that, at 11 weeks gestation only 50% were confirmed, at 12 to 14 weeks the percentage of correct predictions had an increase.

As the baby develops, the genital tubercle is formed fully at around 14 weeks gestation.

Male Nubs

Male nub. (Confirmed by The Nubologists.)

A developing male nub varies at different gestations, the sex will usually be easier to predict if the nub is seen to be imaging at 30 degrees or higher in relation to your baby's spine.

The most common boy nub is usually shown with 'stacking', this is seen as a white blob or a shadow sitting above the white line which indicates developing penis with developing scrotum underneath. Stacking or a rising nub is what gives the angle for a male fetus.

Examples of different male nub shots below.

A rising male nub shot. (Both confirmed by The Nubologists.)

See below for a clear male nub shot, the most common for predicting a baby boy.

Penis and scrotum can be seen clearly with this nub shot. (Confirmed by The Nubologists.)

Female Nubs

A female nub. (Confirmed by The Nubologists.

A developing female nub also varies at different gestations, the sex will usually be easier to predict if the nub is seen to be imaging at 30 degrees less in relation to your baby's spine.

Gestation plays a huge part in predicting a baby girl, the nub can be seen hanging off the end of the rump pointing downwards or sometimes shooting off the end of the baby also known as a 'rocket nub'.

Examples of different female nub shots below.

A female nub. (Confirmed by The Nubologists.)

A female nub hanging off the rump of baby. (Confirmed by The Nubologists.)

A nub shot known as a 'rocket nub'. (Confirmed by The Nubologists.)

Early Gestation

At 11 weeks gestation it is way too early to predict your baby's sex. All nubs start off looking long, smooth tubular and around 12 weeks gestation when the genitals start to form. This is why your baby's sex won't be identified until at a later stage.

The development happens at a fast pace - If you have a scan within a few days of each other, you may not be able to tell the sex on the first ultrasound scan, but at your next scan you would be able to see some significant development and the nub may be a lot clearer.

Throughout an earlier gestation (11 weeks to an early 12 weeks) your baby's nub may looked 'forked', this is how a earlier nub usually looks.

A forked nub is often mistaken to be a girl, when that's not always the case, it's just an under developed nub. This can be seen in both sexe's.

Example of a 'forked' nub. (Confirmed by The Nubologists.)

Let's take a closer look at a picture showing the genital tubercle at 11 weeks gestation. You can tell how similar both nub's look before development.

Picture credit: Majorie England

Picture credit: Science Source

Later Gestation Development

Now we have covered 'The Nub Theory' and shown you the development of a nub you must be wondering how the genitals look fully formed?

You will find at your sexing scan the sonographer may confirm your baby's sex by a 'potty shot' which is looking underneath the baby showing inbetween the legs. Some sonographer's will then confirm sex by a side profile shot. What does that look like? Well, let's take a look.

Male and female side profile genital shots - 20 weeks gestation

A lot of people who are unfamiliar with ultrasound images will presume 3 lines mean you're having a female, We can assure you that male's can also image with 3 lines, being the head of the penis or the scrotum.

(don't forget your ultrasound is made up of lines!)

Now let's have a look at a 'potty shot' to see what a male and female fetus images like and what you can expect to see at your sexing scan or anomaly scan - also known as your 20 week scan.

Please remember that the anomaly scan is not a sexing scan, it is to check that your baby is healthy and growing correctly. Not all sonographers will show you your baby's sex at this scan.