Characteristics of the Unborn Child

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:

• 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).

The normal development of the unborn child depends on many factors.

The unborn child is 10,000 times larger than the original fertilized egg. The heart is pumping increasing quantities of blood through the circulatory system. The placenta forms a unique barrier that keeps the mother's blood separate while allowing food and oxygen to pass through to the child.

4 Weeks Gestation
• 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 one ounce.
• The length is less than 1/8 inch.

6 Weeks Gestation
• The lungs are beginning to form.
• Brain activity can be recorded.
• Eyes are present, but no eyelids yet.
• The heart is more developed and is beating.
• Early reflexes develop.
• The hands and feet have fingers and toes, but may still be webbed.
• The length is less than 1/4 inch.

8 Weeks Gestation
• All essential organs have begun to form.
• Elbows and toes are visible.
• The fingers have grown to the first joint.
• Facial features — the eyes, nose, lips, and tongue — continue to develop.
• The outer ears begin to take shape.
• Organs begin to be controlled by the brain.
• The length is about 1/2 to 3/4 inch.

10 Weeks Gestation
• The unborn child is now called a fetus, rather than an embryo.
• The head is half the length of the body.
• The arms and legs are long and thin.
• The hands can make a fist with fingers.
• Red blood cells are produced.
• The length is about 1 1/4 to 1 3/4 inches.

12 Weeks Gestation
• The neck is present and the face well formed.
• The eyelids close and will reopen at about 24 weeks.
• Tooth buds appear.
• The arms and legs move.
• All body parts and organs are present.
• The fibers that carry pain to the brain are developed; however, it is unknown if the unborn child is able to experience sensations such as pain.
• Definitive signs of male and female gender are present.
• A heartbeat can be heard with electronic devices.
• The length is about 2 to 3 inches.

14 Weeks Gestation
• The skin is almost transparent.
• The mouth makes sucking motions.
• Amniotic fluid is swallowed.
• Sweat glands develop.
• The liver and pancreas are starting to work.
• The length is about 3 to 4 inches.

16 Weeks Gestation
• Swallowing and chest movements are clearly present.
• Movement may be felt by the mother.
• The head and body become proportional.
• The neck takes shape.
• The weight is about five ounces.
• The length is about 4 to 5 inches.

18 Weeks Gestation
• The arms and legs begin to punch and kick.
• The fingernails are well formed.
• The unborn child can suck its thumb.
• Taste buds are present.
• Male or female gender is evident.
• A protective waxy coating is present on the skin.
• The length is about 5 to 6 inches.

20 Weeks Gestation
• Some experts have concluded that the unborn child is probably able to feel pain.
• The skin becomes less transparent as fat begins to deposit.
• Eyebrows and lashes appear.
• Breathing-like movements become regular and are detected by ultrasound, but the lungs have not developed enough to permit survival if birth occurs.
• The unborn child turns its entire body side to side and front to back.
• The length is about 6 to 7 inches.

22 Weeks Gestation
• Rapid brain growth continues.
• The eyebrows and eyelashes are well formed.
• The eyes are fully functional and capable of movement.
• The vocal cords are active.
• Reflexes are present.
• There is little chance for survival outside the uterus.
• The weight is about one pound.
• The length is about 7 to 8 inches.

24 Weeks Gestation
• Unique footprints and fingerprints are present.
• Outside sounds can be heard.
• Actions such as hiccuping, squinting, smiling, and frowning may be seen through ultrasound.
• The lungs have developed such that some premature babies may survive.
• Surviving premature babies may have severe disabilities and require long-term intensive care.
• The weight is about 1 to 1 1/2 pounds.
• The length is about 8 to 9 inches.

26 Weeks Gestation
• The central nervous system is developed enough to control some body functions.
• The eyelids open, close and can perceive light.
• The lungs have further matured and breathing is possible.
• The unborn child exercises muscles by kicking and stretching.
• The weight is about 1 1/2 to 2 pounds.
• The length is about 9 to 10 inches.

28 Weeks Gestation
• Brain-wave patterns resemble those of a full term baby.
• Another person can hear a heartbeat by listening to the pregnant woman's abdomen.
• There is a good chance of survival if birth occurs at this stage of development.
• The weight is about 2 to 2 1/4 pounds.
• The length is about 10 to 13 inches.

30 Weeks Gestation
• The central nervous system has increased control over body functions.
• Rhythmic breathing movements occur.
• The lungs are not fully mature.
• The bones are fully developed, but still soft and pliable.
• The weight is about 2 1/2 to 3 pounds.
• The length is about 15 to 16 inches.

32 Weeks Gestation
• The lungs are still developing.
• Body temperature is partially under control.
• The skin is thicker, with more color.
• The connections between the nerve cells in the brain have increased.
• There is a good chance of long-term survival and the risk of long-term disability is low.
• The weight is about 3 to 3 3/4 pounds.
• The length is about 16 to 17 inches.

34 Weeks Gestation
• The ears have begun to hold shape.
• The eyes open during alert times and close during sleep.
• There is a very good chance of survival with a low chance for long-term disability.
• The weight is about 4 to 4 1/2 pounds.
• The length is about 17 to 18 inches.

36 Weeks Gestation
• Fine hair begins to disappear.
• Body fat has increased.
• The fingernails reach the end of the fingertips.
• The chance of survival is excellent, but the newborn may require special medical care.
• The weight is about 5 to 6 pounds.
• The length is about 16 to 19 inches.

38 Weeks Gestation
• A newborn is considered full-term at 38 weeks.
• The fingernails extend beyond the fingertips.
• Small breast buds are present on both sexes.
• The unborn child can grasp firmly.
• The unborn child turns toward a light source.
• The average weight is greater than 6 pounds.
• The length is about 19 to 21 inches.

Information on this page is reprinted with permission by the Texas Department of State Health Services, from the "A Woman's Right to Know" booklet, copyright 2003 Texas Department of Health. All rights reserved.