"Sex" vs "gender": what's the difference?
We called this site Nub Gender Reveal because that's the phrase people search for. But it's worth being precise about what Kay is actually predicting, because "sex" and "gender" aren't interchangeable words.
The short version
Sex usually refers to biological characteristics, chromosomes, hormones, and anatomy, including the genital tubercle Kay looks at on your scan. Gender is broader: it's the identity a person holds, and often the social role and expression that goes along with it. The two overlap for most people, but they're not the same measurement, and only one of them shows up on an ultrasound.
What Kay is actually predicting
Nub theory and skull theory both look at physical anatomy visible on a scan. That means Kay is predicting biological sex characteristics, not gender. Nobody, not Kay, not a sonographer, not a NIPT test, can scan a fetus and tell you who that person will grow up to be. We use "gender reveal" in our name because it's the familiar phrase, but "sex prediction" is the more accurate one.
An anthropological view
It's not just a modern semantic quibble, either. Anthropologists have documented for decades that plenty of cultures have never worked with a strict two-category system in the first place. Hijra communities in South Asia, Two-Spirit identities held by many Indigenous nations in North America, muxe in Oaxaca, Mexico, fa'afafine in Samoa, and māhū in Hawaii and Tahiti are all long-standing social categories that sit outside a simple male/female split, some with centuries of documented history and specific ceremonial or family roles attached to them. Researchers do debate how well the umbrella phrase "third gender" actually fits each of these, since it's a label anthropologists applied from the outside, and several of these traditions describe themselves in their own terms rather than as a variation on a Western binary. Either way, it's a useful reminder that treating "sex" and "gender" as one and the same thing is a fairly recent, fairly local habit, not a universal rule.
Why it still matters for a site like ours
None of this changes what we're offering: a bit of fun with a scan photo and two folklore-based theories. But it's the reason we're careful with our own wording where it counts, on the order form, in our methods pages, and here. If you take one thing from this page, it's that a percentage on pink or blue is a guess about anatomy, nothing more.