When a sperm cell has combined with an egg cell, the woman is pregnant. She will be pregnant for about 40 weeks until she gives birth. When a girl reaches puberty and her ovaries start to produce egg cells, she can get pregnant if she has sexual intercourse. This can also happen before she has had her first period. You will usually discover that you are pregnant when your period doesn’t come. You can buy a pregnancy test at the chemist’s to find out if you are pregnant or not.