Prenatal Stage

The period from conception to birth is called the prenatal period, and it typically lasts about 40 weeks. Development during this stage is guided by the genetic blueprint inherited at conception, but is also shaped by environmental factors from the very start, so both genetic and environmental influences operate together throughout the prenatal period. Prenatal development can be affected by a range of maternal characteristics, including the mother's age, nutrition, and emotional state during pregnancy. Disease or infection carried by the mother can seriously affect the developing child — conditions such as rubella (German measles), genital herpes, and HIV are believed to be capable of causing genetic and developmental problems in the newborn. A further, distinct source of risk is posed by teratogens — environmental agents that cause deviations from normal development, which can in turn lead to serious abnormalities or even death. Common teratogens include drugs such as marijuana, heroin and cocaine, as well as alcohol and tobacco, all of which can seriously harm the developing foetus and raise the risk of congenital abnormalities when used by a pregnant woman; radiation, such as from X-rays, and certain i …