A woman is born with all the eggs she will ever have. Men begin producing sperm at puberty. It's only until after conception the egg and sperm are both inside the woman.
The zygote is the fertilized egg. It enters a 2-week period of rapid cell division and develops into an embryo.
The zygote now becomes an embryo. The embryo is the developing human from 2 weeks after fertilization through the second month. The placenta also begins to form, which transfers nutrients from the mother to the embryo.
By 9 weeks after conception, the embryo begins to look human-like. The human inside the mother finally begins to look like a baby.
Teratogens, such as chemicals and viruses, that reach the fetus during prenatal development cause harm to the baby. Other abnormalities can be caused by alcohol (fetal alcohol syndrome. All of these things affect the mother's baby.
After going through all of the prenatal development stages and with the effects of teratogens, the baby comes out with a lot of abnormalities and is harmed.