Sperm cells surround an egg, which leads to the fusing of the two, creating a single cell. The cell, then subdivides again and again to soon create a human being.
Zygote and Embryo
A fertilized egg is called a zygote. It enters a two-week period of rapid cell division and develops into an embryo. An embryo is a developing human organism from about two weeks after fertilization through the 2nd month.
A placenta is a life-link that transfers nutrients and oxygen from mother to embryo.
A fetus is a developing human organism from 9 weeks after conception to birth.
Teratogens, or "monster makers", are agents, such as chemicals and viruses, that can reach the embryo or fetus during prenatal development and cause harm.
Fetal Alcohol Syndrome (FAS)
Physical and cognitive abnormalities in children are caused by a pregnant woman's heavy drinking, in the case of the child having FAS. In severe cases, signs include a small, out-of-proportion head, and abnormal facial features.