5 Minute Read

As a Sonographer of over 15 years, I ask myself about the ‘Nub Theory’ – where have you been all my life!?

I first heard about the ‘Nub Theory’ a couple of years ago. My first instinct was to dismiss this idea as I had not seen it in a textbook, just on social media. Prior to opening Beautiful Beginnings, I only checked the gender at the 19-20 week Anatomy Scan during my clinical job.

Traditionally gender detection happens at the 19-20 week Anatomy Scan. This can be easily done, with experience, by angling the ultrasound probe to see between the baby’s legs. Some people call this the ‘Potty Shot’ view, as we look at the bottom area from underneath. We wait for the legs to open wide enough to determine if either a willy or the labia can be seen.

However, the visual appearance for a girl or boy are dramatically different – the labia appears as three white lines, two of the lines are the outer lips and the third line is the interface as they meet in the middle. For the boy, the testes can be seen next the willy sticking out in the space between the legs at an angle of 30 degrees or more upwards. Real time scanning and angling of the probe is needed to capture the exact view needed to determine the gender. 

Seriously, I never thought I would speak the words ‘labia’ to complete strangers more than 10 times a day! But since opening Beautiful Beginnings this is my reality. I feel it is important to not just reveal the baby’s gender in a memorable way, but to also explain to why I reached that decision, showing evidence.

So how does the ‘Nub Theory’ work?

The ‘Nub Theory’ is a second view to add more certainty when checking baby’s gender. We need to angle the probe to get a true mid line sagittal view which is the same as a good profile shot – focusing attention at baby’s bottom we scan from side to side. At Beautiful Beginnings I have adopted having these 2 reliable methods to check and confidently announce the gender. Year by year new ultrasound machines are released, each time the leap forward in image quality is remarkable. This is the main reason I believe that at 15 weeks accurate gender detection with an experienced Sonographer is possible using the nub theory.

Another question I am often asked is how early do I offer gender determination. At Beautiful Beginnings I prefer to do it from 15 weeks onwards. From 14 weeks gestation and under, baby is too small and the genitalia is underdeveloped to accurately see the gender. In some cases you can see the gender early in an ultrasound scan, but not for every lady and is not always accurate. 

As my position as a Sonographer in a clinical environment, we do get asked to check the gender. I prefer to take the whole scan time assessing the health of baby, rather than to give a less than accurate opinion on gender as appointment times can be a constraint. This is why you may be left leaving your diagnostic ultrasound with 90% accuracy or under. At Beautiful Beginnings we do not conduct any of the head to toe checks, hence I can focus on delivering baby’s gender with accuracy and for you to enjoy the experience of spending time with your baby. 

Below is some examples of the difference between the ‘potty shot’ and the ‘nub shot’ for both genders. 

The labia sticks out a little and points towards the ground.

Girl ‘Potty Shot’
Girl ‘Nub Shot’

The testis and will are a lot more prominent and point at angle of 30 degrees or more upwards.

Boy ‘Potty Shot’
Boy ‘Nub Shot’

In conclusion, I am looking forward to seeing what the next decade of advances in ultrasound will bring. If you have any questions or observations about gender determination, don’t hesitate to ask us.