Two theories, one combined score
None of these started life as science, they started as things sonographers and mums noticed and passed around. We haven't invented anything new here, Kay just applies both consistently and turns the result into a percentage instead of a hunch.
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Nub theory
Looks at the angle of a small bump between the legs, measured against the line of the spine, on your profile scan image.
Read the method →
Skull theory
Looks at the shape of the forehead, jaw and browline in profile, a theory that spread through parenting forums and social media.
Read the method →Why the percentage moves around
Each method gets scored by Kay against your specific image, then weighted by how clearly it could actually be read on that particular scan. A textbook-clear nub shot counts for more than a skull profile caught at an awkward angle. If both methods agree strongly, the score climbs. If they disagree, or the image is too blurry or angled to read properly, the score drops, sometimes below the 75% line, in which case you're told that plainly and you're not charged.
Get your reading, £5