The sexual reproduction is a process that people can experience since teenage through mid-life or longer. It is, basically, the union of two sets of genetic information, one from the mother and one from the father, what makes a baby genetically different from either parent. The fluids that lubricate the woman's vagina and the man's urethra help the reproduction, because it leads the sperm to the uterus after the man's ejaculation. When the semen reaches the base of uterus, the first sperm through succeeds.

After this encounter, the outer-layer of the egg swells, casting away the other sperm. Then, the sperm's nucleus seeks the egg's nucleus. The fertilized egg is now called zygote, and repeated cell divisions are made. The basic structure of the baby is formed in the first two months of pregnancy. It also involves cell migration and the differentiation of cells into the many types found in the baby. Fertilization just occurs when the sperm is deposited in vagina during copulation, few days before or two days after the ovulation, which happens two weeks after the last menstruation.

During pregnancy, the fetus receives its nutrition, antibodies, oxygen and discharges carbon dioxide, urea and other wastes as off the mother, through the placenta, attached to the fetus via umbilical cord. That's why it's important that the pregnant women intakes high biological grade of calories. In this period, the mother has to avoid the exposure to certain chemicals, because they may cause malformations in the developing embryo. Some sexually transmitted diseases (STDs), like gonorrhea and infections by chlamydia, can cause blocking of the tubes and scarring. They are a major cause of infertility.

There's a risk of diseases for those who plan to have a baby through sexual reproduction. The best thing to do is make blood counts and examinations to know if everything is right before having a baby. If the couple tries to have a pregnancy without success, they can look for a doctor to know what's wrong and, then, some artificial methods of reproduction can be done for difficult cases, like in vitro fertilization, where the men's sperms and the woman's eggs are mixed in a culture vessel and replaced later into the mother's uterus, and the Intracytoplasmic Sperm Injection, by directly injecting a single sperm into the egg. If the fertilization succeeds, the baby will come up in 38 weeks time.