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No. Skull theory borrows from forensic anthropology, where experts really can sex an adult skull. But the features they use — brow ridge, squared jaw, mastoid process — develop at puberty under sex hormones. At twelve weeks none of them exists yet, so there is nothing for the scan to show.
Skull theory holds that a blockier skull with a sloping forehead and a squarer jaw indicates a boy, while a rounder skull with a tapered chin indicates a girl. Supporters put its accuracy somewhere between 70% and 95%. No peer-reviewed study supports those figures, and we could not find a study that has tested the method at all.
The underlying observation is real but belongs to a different stage of life. Forensic anthropologists and bioarchaeologists can often determine sex from an adult skull, using the brow ridge, the mastoid process behind the ear, and the shape of the jaw and chin.
Those features are products of puberty. As one bioarchaeologist put it, until you reach maturity, or at least puberty, you simply do not get the sexually dimorphic features of the skull that distinguish males from females. The skeletons of infant boys and girls are not meaningfully different in this way, and a twelve-week fetus is a long way before infancy.
So skull theory is not a weak signal that needs a better scan. It is reading for a difference that has not formed.
Even if the difference existed, a twelve-week profile is a two-dimensional slice through a moving target. Rotate the probe a few degrees and the apparent shape of the skull changes — the forehead steepens, the chin recedes or juts. The ultrasound is not a photograph of a shape; it is a cross-section whose outline depends on the angle it was taken at.
Three things make a coin flip feel like a skill. The base rate is already 50%, so half of all readings are right by default. Readings are usually shared in forums after the person already knows the answer, so the confirming ones get posted and the others quietly do not. And the traits being judged are vague enough that a skull can be described as squarish or roundish after the fact to match whatever the answer turned out to be.
That combination is enough to sustain a method indefinitely without it ever working.
The two methods that do give an answer are a non-invasive prenatal test, which reads placental DNA from a sample of the mother's blood from about nine or ten weeks, and the anatomy scan at eighteen to twenty-two weeks.
There is no evidence that it is. The claimed figures of 70% to 95% do not come from any study we could find, and the anatomical differences the method relies on do not exist before puberty.
Because they are working with adults. The brow ridge, mastoid process and squared jaw they use all develop during puberty under the influence of sex hormones. An infant skull does not carry them, and a twelve-week fetal skull is far earlier still.
Better imaging does not help with a difference that has not developed. A sharper picture of a twelve-week skull is a sharper picture of a skull with no sex-specific features in it.
Half of all guesses are right by chance, and readings tend to be shared after the answer is known. The successes get posted and the misses do not, which makes a 50% method look far better than it is.
At the anatomy scan, usually between eighteen and twenty-two weeks, where a sonographer looks at the genitals directly. Before that, a non-invasive prenatal test from about nine or ten weeks is the reliable option.