The Nub Theory
Theory Or Fact?
If you've been told it's too early to find out your babies gender at a first trimester ultrasound, take a look at the nub theory: it's highly accurate from the 12th week of gestational age.
In early pregnancy, both boys and girls have a genital tubercle which will later become a boy's penis or a girl's clitoris. We call this the nub.
So, if boys and girls both have a genital tubercle at this point, how can we tell them apart? It's the angle of the dangle:
Boy nubs angle upward
Girl nubs lie down flatter
Note that it isn't a theory; it's a known biological fact, and is due to the genital tubercle's development into a penis or a clitoris.
The nub angle can be seen in a profile image of the baby.