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A Woman's Right to Know

Characteristics of an Unborn Child

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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.

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 which may require extended hospital care or long term care outside the hospital. Advances in medicine and science will hopefully continue to improve the chances for survival for even the smallest babies.

The health of the baby is strongly linked to the health of the mother. Healthy babies are born to women who are healthy before getting pregnant. Avoiding harmful substances before and during pregnancy is the best way to prevent birth defects and to have the healthiest baby.

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 fetus is most likely to be affected by things like:

  • Alcohol
  • 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)
  • Foods with high mercury levels

Gestation Periods

Weeks:  4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 26 | 28 | 30 | 32 | 34 | 36 | 38 | 40

4 weeks

Four Weeks

  • The brain and the spinal cord begin to form
  • The heart begins to form
  • The stomach and intestines are forming
  • Bone tissue is growing
  • The eyes and ears are just beginning to form
  • The weight is less than 1 ounce
  • The length is less than 1/8 inch