The reproductive system allows humans to reproduce. The male reproductive system produces sperm through organs like the testes and penis. The female reproductive system produces eggs through organs like the ovaries, uterus, fallopian tubes, vagina and vulva. Fertilization occurs when an egg and sperm join to create an embryo. Pregnancy is when the embryo develops into a fetus inside the uterus, receiving nutrients from the mother through the placenta. Birth happens after 9 months of pregnancy, when contractions push the fetus out through the vagina.