Another method we have discovered for gender identification is by examining certain features of the baby's skull. Some people claim that it is possible to determine the sex of a baby based on these features, but this is highly inaccurate.
According to this theory, there are observable differences between the male and female skull. It suggests that the male cranial mass is more block-shaped and larger, while females have narrower jawlines and more rounded lower jaw bones. However, these distinctions only become apparent after reaching maturity.
If you watch an ultrasound video on YouTube, you will notice that the shape of the head appears to "change" depending on the depth to which the ultrasound waves penetrate. Once the scan reaches a halfway point through the baby (usually seen by observing the nose bone in a mid-line sagittal plane), all skulls appear the same.
It is important to note that anyone claiming to identify gender differences in an ultrasound image is simply joking or misleading you. The Skull Theory is essentially a coin toss, with a 50:50 chance of being accurate.
Hence, I prefer to rely on the Nub Method when determining the gender of babies. In my own years of experience, the Nub Method has proven to be highly accurate. Feel free to try it out yourself, but remember not to solely rely on this theory.