What is typically the first sign of sexual maturation in females?

The first sign of sexual maturation in females is breast development. This process, known as thelarche, typically occurs during the early stages of puberty and signifies the onset of sexual development. Breast development is initiated by hormonal changes, particularly the increase in estrogen levels, which play a crucial role in developing secondary sexual characteristics. This physical change is a key milestone in a young girl's transition into adolescence and serves as an indicator of her body's readiness for further sexual development.

Menstruation, while an important event in puberty, typically occurs later in the developmental process after breast development and other changes, such as the growth of pubic hair. Additionally, the growth of axillary hair follows these earlier physical changes as maturation continues. Thus, breast development is the most foundational and earliest visible sign of sexual maturation among the options provided.