If you're keen to know your baby's sex as soon as possible and just can't wait until the 20-week scan, skull theory is a gender prediction test that claims to be able to reveal your baby's sex based on their skull shape and size as seen in the 12-week scan (your first routine scan, which is actually a dating scan).


" The ‘skull’ theory relies on ultrasound assessment of the baby’s facial bony features and the skull," Professor Christoph Lees, Consultant Obstetrician and Spokesperson for the Royal College of Obstetricians and Gynaecologists told MadeForMums.

How accurate is skull theory?

The basic premise of skull theory is that men have squarer, stockier and bigger heads than women, and, so the theory goes, these differences may be spotted in the womb. The main differences are:

1. A man's head is blockier and bigger than a woman's head.

2. The temporal ridge, which runs along the outer side of the top of the skull, is squarer on a man than a woman.

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3. The ridge above a woman's eye sockets is sharp, while the man's is rounder.

4. Cheekbones are more pronounced on a male skull than a female one.

5. The male skull has a square jawbone: the woman's skull has a rounder one.

6. The male forehead is lower and more sloping.

Skull theory - boy and girl examples


These skull theory ultrasound comparisons show a boy example of skull theory (on the left) and a girl example of skull theory (on the right). We can can see that the boy's head here does look bigger and squarer than the girl's.

So does skull theory work?

Unfortunately the science on this one is more than a little shaky. For starters, the human skull continues to form and grow well beyond the womb.

Add to this the fact that skulls actually vary greatly between different racial groups too, as well as between the sexes - and the substance falls away from the argument pretty much altogether.

Kristina Killgrove, a bioarchaeologist at the University of West Florida says that, simply put, the theory makes no sense whatsoever.

'Until you get to maturity or at least puberty you just don't get these sexually dimorphic features of the skulls in males and females.'

In other words, while there may well be clear differences between a grown male and grown female skull, it's very hard to see how these features could relate to an unborn baby.

Professor Lees agrees, saying: "There is no scientific evidence that it works."


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Tara BreathnachContent Editor and Social Media Producer

Tara is mum to 1 daughter, Bodhi Rae, and has worked as Content Editor and Social Media Producer at MadeForMums since 2015