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

When you’re sitting with 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 method”, “gender guess scan”, “early gender scan” and “boy or girl scan” are among the most popular with pregnant women in Denmark. That says everything about how curious we get while we’re waiting!

So here is a guide to the best-known methods for guessing the baby’s sex from early scan images. Both the popular ones, the funny ones and the slightly nerdy ones. Remember! No method is 100% certain, but it’s fun to guess. ☺️

Why do so many people try to guess the baby’s sex from scans?

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

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

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

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

When: week 6–8

What is the method about?
You look at which side the placenta is forming on in the very first weeks of scanning.

The 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 hard to see clearly
• There is no solid scientific evidence

The Ramzi method is 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

The theory says:

• Boy: pronounced forehead, more square skull
• Girl: rounder skull, softer lines

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

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

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

(also called the “Genital Tubercle Theory”)

When: weeks 11–13 (typically the nuchal translucency scan)

Nub Theory is by far the most popular and most accurate method for gender determination 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 genital nub).

So what exactly is the nub?

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

• penis (in boys), or
• the clitoris and labia (in girls)

This development is controlled by hormones, especially testosterone in boys.
It’s the hormonal influence that makes the nub start to change direction and structure.

How the nub changes:

• In weeks 10–11 it’s almost neutral for both sexes
• In week 11–12 the boy nub starts to rise upward at a clear angle
• In week 12–13 the girl nub remains more horizontal and smooth

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

⭐ How to read the nub:

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

🔹 Girl:

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

It often is:

• smooth
• nice
• a little longer
• more streamlined

🔹 Boy:

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

It can be:

• thicker
• shorter
• more of a “rocket shape”
• more pronounced

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

⭐ Why does Nub Theory work so well?

Because the direction of the genital nub is influenced by early hormonal exposure, which already differs between boys and girls from week 11 onwards.

• Boy → testosterone causes the tubercle to lift
• Girl → absence of testosterone → the tubercle remains horizontal

So there is a real biological difference, and not just a “guessing game.”

⭐ Accuracy: up to 90% with clear images

When these criteria are met:

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

… the accuracy, when read by an expert, is estimated to be:

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

That’s why many private scan clinics use this method.

⭐ What can be misleading in Nub Theory?

There are three major pitfalls:

1. Rotation error

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

→ 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 and more upward-pointing structure.

→ “Fake boy” (a boy “in disguise”).

⭐ How do you get the best nub shot?

• Make sure you get 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 can’t unsee it.

⭐ Why do mums love the Nub Theory?

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

• It’s concrete
• It’s “nerdy” in a fun way
• It creates a sense of community (moms guess for each other)
• It makes the wait feel shorter
• It’s surprisingly often right

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

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

And then there are all the old, cozy and completely unscientific gender myths that every pregnant woman hears. They don’t work, but they live on because they’re fun, relatable, and perfect for guessing. 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

• Lots of nausea, especially in the 1st trimester → girl
• Almost no nausea → boy

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

3. “Girls steal their mother’s beauty”

• More blemished skin, pigmentation, oily 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 has been passed down for generations and is a hit at baby showers.

How to do it:

1. Find a ring (preferably gold, for example a wedding ring).
2. Tie it to a string or a lock of hair (if you want it to feel 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
• Circular movements → girl

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

7. High bump vs. low bump

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

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

8. The dream myth

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

(One of the most shareable myths – and it often turns out right purely by coincidence.)

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

A TikTok favourite.

The myth says:

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

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

These myths are not something you should rely on, but they’re 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 quite accurate (especially Nub / Genital Tubercle), while others are pure entertainment.

Make the wait cozy while you wait for the final answer

The wait 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 your 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 for birth and your baby’s arrival. They help you find calm when your thoughts are spinning, and remind you that your body is working even when you can’t feel it.
👉 See the affirmation cards here

Pregnancy bola

A bola is a piece of jewelry you wear during pregnancy. It emits a soft, chiming sound that many babies recognize after birth. It’s a lovely way to create a small connection to your 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 your 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 keep it light-hearted

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

Your baby will be wonderful and amazing no matter their sex. Guessing games are part of the magical waiting time and a lovely way to bond with your baby.