Can the fetus nub change after 12 weeks?

Yes, the fetus nub, which is the genital tubercle, can change position and appearance after 12 weeks of gestation. While the nub is often used to predict the sex of the fetus during early ultrasounds, its definitive morphology becomes more pronounced as pregnancy progresses. By around 12 weeks, the nub may start to show characteristics associated with either male or female genitalia, but definitive sex identification is typically clearer after 16-20 weeks.