A guide to the Nub Theory, the Ramzi method, Skull Theory and magical myths

When you’re holding an early scan image of your baby, it’s almost impossible not to zoom in on every tiny detail. You look for signs, angles, shadows. Everything that might reveal whether it’s a boy or a girl.

And you’re far from alone.

Searches like “nub theory”, “ramzi metode”, “gætte køn scanning”, “kønsbestemmelse tidlig scanning” and “dreng eller pige scanning” are among the most popular among pregnant people in Denmark. That says everything about how curious we become while we wait!

Here you will find a guide to the most well-known methods for guessing the gender from early scan images. Both the popular, the fun, and the slightly nerdy ones. Remember! No method is 100% certain, but it's fun to guess. ☺️

Why do so many try to guess the gender from scans?

It’s rarely about colours or clothes.
It’s about:

• to bond with your baby, to get to know this little human being
• to make the waiting time more fun
• to get a sense of "who" is in there
• sharing something with your partner
  
• Get ideas for baby names

It’s almost a mini ritual:
You send pictures around. Everyone has an opinion. You guess. You laugh. And even though none of the methods are 100% reliable, it’s a cosy way to enjoy the anticipation while you wait. This article is perfect to share with friends, your partner, your mum and your mums’ group when you want to guess together.

⭐ 1. Ramzi method – the most debated (and early!)

When: week 6–8

What is the method about? You look at which side the placenta is placed on in the very first scan weeks.

Theory says:

• Placenta on the right side → boy
• Placenta on the left side → girl

Challenges:

• Early scans are mirrored depending on the method – remember to ask the person doing the scan
• Placement can be difficult to see clearly
• There is no solid scientific evidence

The Ramzi method is therefore mostly just for fun, but it’s fantastic as a conversation starter and as a “first guess”, because you can use it very early on.

⭐ 2. Skull Theory: guess the sex from the shape of the skull

When: from week 11 and all the way up to week 20

Theory says:

• Boy: prominent forehead, more square-shaped skull
• Girl: rounder skull, softer lines

It sounds simple, but in practice it’s a subjective method, because the shape of the fetal skull can vary enormously from week to week.

But as a “just-for-fun method” it works really well, especially when you compare pictures in your group of friends.

⭐3. Nub Theory: most accurate method before week 14

(also called the “Genital Tubercle Theory”)

When: week 11–13 (typically nuchal translucency scan)

Nub Theory is by far the most popular and most accurate method for gender prediction before week 14. What many don’t know is that Nub Theory is simply the “popular” version of the medical method used for early gender determination: Genital Tubercle Theory.
The two terms describe exactly the same method: reading the angle of the genital tubercle (the nub).

What exactly is the nub?

All fetuses, both boys and girls, look identical in weeks 10–11.
The genital tubercle (nub) is a small raised structure between the baby's legs, which later develops into either:

• penis (for boys), or
• clitoris and labia (for girls)

This development is controlled by hormones, especially testosterone in boys.
It is the hormonal influence that causes the nub to begin changing direction and structure.

How the nub changes:

• In weeks 10–11 it is almost neutral in both sexes
• In weeks 11–12 the boy nub starts to rise upwards at a clear angle
• In weeks 12–13 the girl nub stays more horizontal and smooth

That’s why weeks 12–13 are the perfect time to read the gender.

⭐ How to read the nub:

This is the basic rule in the Nub Theory / Genital Tubercle Theory:

🔹 Girl:

The nub lies horizontally, in a parallel line with the spine
→ angle of under approx. 30°

It is often:

• smooth
• fine
• a little longer
• more streamlined

🔹 Boy:

The nub points upwards at a clear angle
→ angle of over 30°

It can be:

• thicker
• shorter
• more "rocket shape"
• more pronounced

This is the most accurate gender prediction you can make before week 14.

⭐ Why does the Nub Theory work so well?

Because the direction of the genital tubercle is influenced by early hormonal influence, which is already different in boys and girls from week 11 onwards.

• Boy → testosterone leads to a rise in the tubercle
• Girl → absence of testosterone → the tubercle remains horizontal

So there really is a biological difference – it’s not just a “guessing game”.

⭐ Accuracy: up to 90% with clear images

When these criteria are met:

• clear profile
• correct age (12–13 weeks)
• the nub is visible and not covered
• no rotation of baby

… the accuracy, if read by an expert, is assessed to be:

• 70% in week 11
• 80–90% in week 12–13

That's why many private scanning clinics use this method.

⭐ What can be misleading in the Nub Theory?

There are three major pitfalls:

1. Rotation errors

If baby rotates a little (for example rolls toward the camera), the nub will look as if it’s pointing upward.

→ This is the biggest reason for “boy” guesses on girls.

2. Early scan (10+ or 11+0)

The earlier the scan, the more “neutral” the nub is.

→ People often guess “girl” because the angle can’t be seen yet.

3. Umbilical cord in front of the nub

It can create the illusion of a thicker, more lifted structure.

→ "Trick-boy."

⭐ How do you get the best nub shot?

• Make sure you have a true side view
• If possible, ask the sonographer to take a clean profile shot
• Baby needs to lie still
• Feel free to zoom in at home. The quality is often better than you think
• Feel free to use several images if you have them

Once you know what to look for, you won’t be able to stop.

⭐ Why do mums love Nub Theory?

Because it feels like a secret code in the scan image that you can read:

• It’s concrete
• It's “nerdy” in a fun way
• It creates a sense of community (mums guess for one another)
• It makes the waiting time shorter
• It’s surprisingly often right

It’s not a guarantee, but it’s the most realistic estimate you can get before week 14 without a blood test.

⭐ 4. Fun myths (that don’t work, but that everyone loves to guess from)

And then there are all the old, cozy and completely unscientific gender myths that every pregnant person hears. They don’t work, but they live on because they’re fun, relatable and perfect for guessing games. And remember, every guess has a 50% chance of being right. Number 6 is really fun to try at a baby shower. 😉

Here are the classics:

1. The shape of the bump

• Pointy and carried far forward → boy
• Round and wide side-to-side → girl

(In reality, it’s about anatomy, abdominal muscles and number of pregnancies.)

2. Nausea

• Severe nausea, especially in the 1st trimester → girl
• Hardly any nausea → boy

(The myth is so widespread that many people believe it. Research actually does show a small tendency – but by no means a rule.)

3. “Girls steal their mother’s beauty”

• More blemished skin, pigmentation, greasy hair → girl
• Perfect skin and glow → boy

(A myth, and honestly!? A bit sexist.)

4. Cravings

• Sweet → girl
• Salty and sour cravings → boy

(Cravings are primarily driven by mum’s hormones and blood sugar, but the myth lives on.)

5. Baby’s heart rate

• Over 140 bpm → girl
• Under 140 bpm → boy

(This one is extremely popular, even though studies show zero correlation.)

6. The ring test (ring on a string)

This one is passed down through generations and is a hit at baby showers.

How to do it:

1. Find a ring (preferably gold, e.g., a wedding ring).
2. Tie it to a string or a lock of hair (if you want it to be extra magical).
3. Hold the ring completely still over your belly.
4. Wait a few seconds without moving your hand.
5. See which way the ring starts to swing.

Reading:

• Pendulum back and forth → boy
• Round circular movement → girl

It's not scientific at all, but surprisingly entertaining.

7. Belly high vs. low

• Carried very high → girl
• Low and more “lying” bump → boy

(In reality, it’s about muscles and the baby’s position.)

8. The dream myth

• Dream you’re having a boy → you’ll have a girl
• You dream you’re having a girl → you’ll have a boy

(One of the most shareable myths – and often it actually hits the mark purely by coincidence.)

9. Urine test with baking soda (“baking soda test”)

A TikTok favorite.

The myth says:

• Fizzes when urine hits baking soda → boy
• No reaction → girl

(In reality you’re testing pH value, not gender.)

These myths are not something you should rely on, but they are perfect as a little distraction while you wait and a cosy way to guess together.

⭐ What does the research say?

The only reliable methods for early gender determination are:

• NIPT / blood test (from week 9–10)
• Gender scan (from week 14–16)

All other methods – Nub Theory, Genital Tubercle, Ramzi, Skull Theory – are guessing methods.

Some of them are actually quite accurate (especially Nub / Genital Tubercle), while others are pure entertainment.

Make the waiting time cozy while you wait for the result

The waiting time can feel long, especially when you sit and zoom in on scan images on your phone every evening. But it can also be an opportunity to create small rituals, calm and a bit more everyday self‑care.

Here are some things that can make the days until the next scan a bit easier and cosier:

Affirmation cards for pregnancy

Beautiful cards with calming and empowering phrases you can use while you wait to prepare yourself for birth and baby’s arrival. They help you find calm when your thoughts are spinning, and remind you that your body is working even when you don’t feel it.
👉 See the affirmation cards here

Pregnancy bola

A bola is a piece of jewelry you wear during pregnancy. It emits a gentle, tinkling sound that many babies recognize after birth. It's a nice way to create a little connection to the baby already now, while you're waiting. 👉 See pregnancy bolas here

Organic pregnancy tea

A mild and safe herbal tea that can be enjoyed throughout pregnancy. It’s a cosy little everyday ritual that can bring calm, warmth and presence while you count the days and weeks.
👉 See the pregnancy tea here

Pregnancy ball

Great for the body in the third trimester: relieves the lower back, helps baby down into the pelvis and gives you a better sitting position as you start to feel heavy.
👉 See the pregnancy balls here

Guess away, but take it with a smile

Whether you use Nub Theory, Ramzi, Skull Theory, or feel there's something to the old myths, there's one thing that's always true:

Your baby will be lovely and amazing regardless of their gender. Guessing games are part of the magical waiting time and a delightful way to bond with your child.