Prenatal development occurs in three periods: germinal (0-2 weeks), embryonic (3-8 weeks), and fetal (9 weeks until birth). During the germinal period, conception occurs and the placenta forms for nourishment. In the embryonic period, major organs develop by 8 weeks when the embryo is less than 2 inches. During the fetal period, all body parts are present by 9 weeks, brain development occurs significantly, and viability is usually reached at 22 weeks. Risks to the developing fetus include toxins, illnesses, certain agents, pollution, and maternal stress or depression which can cause birth defects or impair development. The birth process culminates with the newborn's first minutes assessed using the Apgar