There are many theories that claim they can help you determine the sex of your baby, you're bound to come across one of them – for example, we've all heard about the old wives' tales that claim you're having a girl when you carry a high bump, and what about the myth that you're having a boy when you don't experience any morning sickness?
If you're interested in guessing the sex of your baby you may have come across the nub theory and wondered – what exactly is a nub, and more to the point, is nub theory really accurate? We've looked into this and spoken to expert Rachel Fitz-Desorgher, a midwife with 30 years of experience in infant feeding, active births, and working with parents, to reveal the answers to your questions, so keep reading to find out if you can rely on the nub theory, or if it's just another fun guessing game.
What is a nub?
You're probably most curious about the word 'nub' – a nub refers to the unformed reproductive organs, so if you were wondering if it was related to your baby's bits, you guessed right! The nub eventually grows into either the clitoris and labia or the penis and scrotum, depending on the sex of your child.
What is the nub theory?
The nub theory is an interesting concept, we'll give it that! It looks at the early development of the genitalia while the foetus is still growing in your womb to try and determine the sex of the baby. This isn't as straightforward as it sounds, as the nub looks very similar at this stage on both boys and girls. It's also important to note that this is not a science-based theory.
How does the nub theory work?
According to the nub theory, you can use your 12-week scan (which determines your due date) as a tool for predicting the sex of your baby. From around 12 weeks to 14 weeks you'll be able to clearly see your baby's nub, or genital tubercle. Both males and females have it, and it will eventually develop into the penis and scrotum if it is a boy, or the clitoris and labia if it is a girl. It isn't the shape or appearance of the nub itself that is meant to signify the fetuss sex at this stage, but instead, the angle at which it points upward.
Midwife Rachel Fitz-Desorgher says the nub theory is sometimes referred to as "looking at the ‘angle of the dangle’", and explains that; "some people claim that when you look at an early scan of the baby’s genital area, although both girls and boys have identical-looking little bobbles (or ‘nubs’), the male ‘nub’ sticks up at a different angle from the female ‘nub’.” – Essentially, Rachel is saying that the angle of the ‘nub’ in relation to the spine is supposed to tell us if it’s a boy or girl, according to the nub theory.
So if you compare the angle of the nub in relation to the spine, you can try to predict your baby's sex. If the nub is angled at 30 degrees or more it is likely a boy, and if it is under 30 degrees it is likely a girl. As you can imagine, predicting the angle of the dangle is tricky to get completely right, even for experts, and this is why you're not normally told baby's gender until 20 weeks of pregnancy.
While the 12-week scan provides a lot of information, it doesn't tell the whole story. “When you look at a 12-week scan, you can see many things if you are trained to do so,” Rachel says, “but even the very best sonographer will not claim to be able to tell you the sex of your baby with any certainty. The most accurate time to determine the sex of your baby is when your little warm bundle has safely reached your arms!”
Rachel also notes that scanning is first and foremost for safety purposes only, saying; “Scanning is a medical procedure done to confirm pregnancy and exclude abnormalities, and the NICE guidelines support the NHS, providing them for this reason.”
Rachel goes on to point out that; “Many parents go into the room treating the scan as a nicety and want more info than the sonographer can actually give. Sonographers are put under a lot of pressure to look for gender when the sonographer is actually supposed to be concentrating on checking that the baby has all its arms and legs!”
So this is definitely something to be aware of when you go to have your scan.
How accurate is the nub theory?
While the nub theory isn't scientifically-based, a 2015 study has suggested that there could be some truth to this method, particularly in predictions made after 14 weeks gestation. The study tells us that there was an overall success rate of 75% in the first trimester group (11–14 weeks) when predicting the sex of babies using this method – although it is worth noting that there were some scans where a prediction could not be made. Also, the results were less accurate for fetuses younger than 12 weeks, with an overall success rate of only 54%.
However, Rachel advises caution when it comes to relying on this method for determining gender, saying that; “Using the nub theory may be no better than swinging a coin over your tummy, looking at the shape of your bump, analysing your cravings or counting how many times you need to shave your legs in a month.
“As the mum of four boys, my friends tested every one of their favourite gender-prediction theories on me, and I can say categorically that - just like the scientific evidence tells us - none of them worked any better than 50:50. So toss a coin or just guess - it will work just as well!” She advises.
Keep in mind that if you are given a gender prediction at your scan, you should be aware that the results can vary depending on your sonographer's personal experience, as well as the age and sex of the fetus. The position that baby is lying can also effect the accuracy of predictions. At 13 weeks gestation and above you may be able to get an opinion from your sonographer, but it's best not to take it as gospel in order to avoid any surprises or disappointment later.
Predictions prior to 12 weeks are discouraged, and some sonography departments will refuse to give you a prediction under a certain gestational age.
Should I try the nub theory?
You may be excited to glean any information about your upcoming arrival, so you could be tempted to try nub theory for yourself. While it can be a bit of harmless fun to attempt, we recommend not taking the nub theory too seriously, though the accuracy rate sounds pretty good on paper, even the experts can get it wrong.
What other gender theories exist?
If you fancy having a go at some other theories which aim to reveal your baby's gender, take a look at the skull theory and our Chinese Gender Predictor Tool.
But don't rely on these theories to pick your nursery colours. If you're after an accurate prediction it's better to wait until your 20 week anomoly scan and a medical professional has confirmed your baby’s sex.
Meet the experts
Rachel Fitz-Desorgher is an active birth teacher, parenting consultant and author of Baby Skin To Skin, with over 30 years working as a midwife and as a parenting consultant. She has appeared on numerous radio programmes, teaches other midwives and peer supporters, and lectures at hospitals and conferences.
Bryony Firth-Bernard graduated from the University of Gloucestershire with a first in Journalism and went on to work as a reporter at Heart Radio West before becoming the lifestyle intern across Good Housekeeping, Prima and Red magazine.