Many girls worry that they are not developing fast enough, or are concerned if they develop before their friends do. Remember, each person has her own timetable. Some girls start puberty early, and some start later. The main female hormones are estrogen and progesterone. Breasts start to grow when a girl is between 9 and 13.
Many girls are concerned about the size and shape of their breasts.
Breasts come in many different sizes, so girls shouldn't worry if theirs are different from their friends'. Pubic and underarm hair will start to grow next. The lining of the womb, or uterus, starts to thicken. About 2 weeks later, one of the ovaries releases an egg, or ovum. If sperm from a man's body does not join with the egg, that is, it is not fertilized, then the thick lining of the uterus is not needed.