Yes, a girl can get pregnant before she gets her first period. Getting pregnant is related to ovulation. Because a girl can ovulate before having her first period, it is possible to become pregnant if she has sex. Abstinence (not having sex) is the only way to completely prevent STDs or unwanted pregnancy.
Also asked, can you still ovulate and not have a period?
The trouble with having no menstrual cycle is that you don't know if your body is planning to have one in the near future. This means, you could be ovulating in preparation for a cycle that's about to start, or you could be ovulating without having actual periods. Any time you ovulate, you can become pregnant.
Can you get pregnant if you don t have a period at all?
Women who are not menstruating due to a certain condition (i.e. low body weight, breastfeeding, perimenopause, etc…) risk the chance of getting pregnant because ovulation could start again at any point. If you ovulate and do not start your period a couple weeks later, you may want to take a pregnancy test.