Growth and Development
The age of an unborn child is most often defined by gestational age, which is measured from the first day of the last normal menstrual period. Because some women have irregular periods, other ways are also used to help date the pregnancy. One way is to measure the length of the unborn child by ultrasound.
At fertilization (when the male sperm enters the female egg), the unborn child has his or her own unique set of DNA material — or genes — half from the mother and half from the father. The DNA is the blueprint for growth and development of all cells throughout life. DNA determines all of the baby’s physical characteristics such as gender; the shape of the nose and ears; and the color of the hair, eyes, and skin.
During the first 8 weeks, the unborn child is known as an embryo. After that time the unborn child is known as a fetus. It is during the first ten weeks of pregnancy that the unborn child is most likely to be affected by things like:
• nicotine in cigarettes or other tobacco products
• some prescription medicines or over-the-counter drugs
• illegal drugs (like heroin, cocaine, or marijuana
• viruses (like German measles)
• x rays, radiation therapy, or accidental exposure to radiation
• vitamin deficiencies (such as folic acid).
The normal development of the unborn child depends on many factors. This guide will only describe normal growth and development.
Babies born earlier than 37 weeks of pregnancy are called premature or preterm. Babies born between 37 and 42 weeks of pregnancy are called full term. Babies born close to full term have the best chance to survive and do well. The earlier a baby is born, the more likely he or she is to have serious health problems that may require extended hospital care or long-term care outside the hospital. Advances in medicine and science will, it is hoped, continue to improve the chances of survival for even the smallest babies.