Guides & resources

Nub theory, explained properly

Honest, study-backed guides to early gender prediction — how nub theory works, how accurate it really is, and how to read your own 12-week scan.

Pillar guide

What Is Nub Theory? The Complete Guide to Early Gender Prediction

The genital tubercle, the 30-degree rule, accuracy by week, and how to tell a boy nub from a girl nub — the definitive, study-backed guide.

How Accurate Is Nub Theory? A Study-by-Study Breakdown

The honest, study-backed answer on nub theory accuracy: realistic numbers by week, why the “99%” claims mislead, and what happens if a prediction is wrong.

Boy Nub vs Girl Nub: How to Tell the Difference on a 12-Week Scan

The angle, the shape, and the stacking sign that separate a boy nub from a girl nub — with a side-by-side comparison table and the mistakes that catch most parents out.

The Stacking Sign in Nub Theory Explained

What the “stacking sign” looks like, why those layered lines lean boy, how it pairs with the 30° angle, and why it is so easy to miss at home.

How to Read Your 12-Week Scan for Gender (Nub Theory)

Fresh from your dating scan? Learn how to spot the nub, measure the angle, read the shape, and avoid the common cord mix-up — step by step.

The Best Week for Nub Theory: When to Get a Nub Reading

Why 12–13 weeks is the sweet spot for a nub reading, what 11 weeks and 14+ weeks really look like, and what to do if your scan is earlier than 12 weeks.

Can You Tell the Gender at 12 Weeks? What the Scan Can (and Can’t) Show

The 12-week scan is a dating scan, not a gender scan — but nub theory can still read sex at ~85–90% from a clear image. What’s realistic, and what to do next.

Nub Theory vs Ramzi vs Skull Theory: Which Is Most Accurate?

An evidence-honest comparison of nub, Ramzi and skull theory — accuracy, earliest week, and which one is actually backed by science.

NIPT vs Nub Theory: Which Early Gender Test Should You Choose?

A blood test or your existing scan? Compare NIPT and nub theory on timing, accuracy, cost, and effort — and see why many parents do both.

Does Nub Theory Work for Twins? A Realistic Guide

Nub theory applies the same 30° rule to each twin — but crowding and position make twins harder to read. What a good twin scan looks like, and what to do if only one baby can be called.

How Our AI Predicts Baby Gender From Your Ultrasound

AI reads the nub consistently; a human double-check catches the edge cases. Here is exactly how NubHub combines both — plus what the research really says.

Creative Gender Reveal Ideas After an Early Prediction

Ten warm, do-anywhere gender reveal ideas to celebrate your early prediction — balloon boxes, scratch cards, cake surprises, and sweet ways to tell siblings and grandparents.

Nub Theory FAQ: Your Questions About Early Gender Prediction

How nub theory works, when it’s accurate, boy vs girl signs, comparisons with Ramzi/skull/NIPT, and how NubHub’s AI + human double-check work — answered in plain English.