Your first period is a sign that your body is changing, and that it’s now possible for you to get pregnant. For a pregnancy to happen, a sperm cell needs to fertilize an egg in the fallopian tube (for example, during penis-in-vagina sex). If the egg is not fertilized during the ovulation stage, then the uterus lining sheds and flows out of the vagina as a period.
You can only get pregnant if a sperm cell (from a penis) fertilizes the egg. This can happen even if you haven’t had your first period yet, because ovulation and the growth of the uterine lining both happen in the weeks before your first period.
When a person does get pregnant, the fertilized egg implants in the thickened uterine lining, and that lining stays inside. Then, the cycle of ovulation and menstruation is paused. This means that when someone is pregnant, their periods will stop for the duration of the pregnancy.
Just because you are physically able to get pregnant, that doesn’t mean you’re ready to have a baby. If you want to talk about this more, reach out to your parent, caregiver, or another trusted adult.