In spite of the fact that the first developmental period in the life span is next to the shortest of all – the shortest is the period of the newborn or infancy – it is in many respects one of the most, if not the most, important period of all. This period, which begins at conception and ends at birth, is approximately 270 to 280 days in length, or nine calendar months.

Although it is relatively short, the prenatal period has six important characteristics, each of which has a lasting effect on development during the life span. They are as follows:

  1. The hereditary endowment, which serves as the foundation for later development, is fixed, once and for all, all this time. While favourable or unfavourable conditions both before and after birth may and probably will affect to some extent the physical and psychological traits that make up this hereditary endowment, the changes will be quantitative not qualitative.
  2. Favorable conditions in the mother’s body can foster the development of hereditary potentials while unfavourable conditions can stunt their development, even to the point of distorting the pattern of future development. At few if any other times in the life span are hereditary potentials so influenced by environmental conditions as they are during the prenatal period.
  3. The gender of the newly created individual is fixed at the time of conception and conditions within the mother’s body will not affect it; as is true of the hereditary endowment. Except when surgery is used in gender transformation operations, the gender of the individual, determined at the time of conception, will not change. Such operations are rare and only partially successful.
  4. Proportionally greater growth and development take place during the prenatal period than at any other time throughout the individual’s entire life. During the nine months before birth, the individual grows from a microscopically small cell to an infant who measures approximately twenty inches in length and weighs, on the average, 7 pounds. It has been estimated that weight during this time increases eleven million times. Development is likewise phenomenally rapid. From a cell that is round in shape, all the bodily features, both external and internal, of the human being develop at this time. At birth, the newly born infant can be recognized as human even though many of the external features are proportionally different from those of an older child, an adolescent, or an adult.
  5. The prenatal period is a time of many hazards, both physical and psychological. While it cannot be claimed that it is the most hazardous period in the entire life span – many believe that infancy is more hazardous – it certainly is a time when environmental or psychological hazards can have a marked effect on the pattern of later development or may even bring development to an end.
  6. The prenatal period is the time when significant people from attitudes toward newly created individuals. These attitudes will have a marked influence on the way these individuals are treated, especially during their early, formative years. If the attitudes are heavily emotionally weighted, they can and often do play havoc with the mother’s homeostasis and, by so doing, upset the conditions in the mother’s body that are essential to the normal development of the newly created individual.