From the moment of conception to delivery, the development of a child in the womb is a remarkable process. Within nine months, a singular microscopic cell will divide and differentiate within the protective environment of the womb, completely dependent on it for survival. The tiny fetus will change and grow into a breathing, seeing, hearing, thinking baby, separate from the mother, but still relying on her for care.
Initial Development
The fertilized egg will first embed itself in the lining of the uterus, known as the placenta. This will provide a place for the egg to grow and be protected. The blood-rich tissue will nourish the egg as its cells multiply. Then the embryonic period begins. As the embryo grows, the umbilical cord will form, connecting the baby to the placenta.
First Trimester
The embryo forms three layers of cells. The outer layer will form the skin, nervous system, eyes, inner ears and connective tissues. The middle layer will eventually become bones, muscles, kidneys and reproductive organs. The inner cells will develop into lungs, intestines and bladder.
Growth is rapid during this time. The cells continue to divide and differentiate. As the embryo develops, facial features will form. Small buds will also form on the body, which will eventually become the arms and legs. The embryo will also begin to move on its own.
By the end of the first trimester, the embryo will have a distinct face and head, arms and legs with feet and tiny toes. The genitalia also have begun forming. By this time, the baby will be around 2.5 inches long.
Second Trimester
In the second trimester, the skeleton will develop rapidly, providing a framework for other growth. The organs within the body also continue to grow, and fat deposits develop. The immune system will form. Hair, fingerprints and fingernails also begin to grow.
During this time, the baby will experience sleep. It will also start hearing, swallowing and exploring its environment with its hands. By the end of the second trimester, the baby will be around 9 inches long, weighing around 2 pounds.
Third Trimester
In the third trimester, the baby will put on more weight, gaining fat that will smooth out any wrinkles in the skin. The baby will also begin to breath the surrounding fluid in the womb. Its eyelids will open, and the eyes will dilate and begin to detect light. Movement of the baby will become more noticeable and may even be visible from the outside.
Preparing for Delivery
As delivery approaches, a thick, pasty coating will form on the baby. Called the vernix caseosa, it protects the baby's skin. Space will become crowded in the womb as the baby continues to grow. The organs will be able to work on their own. The baby will have gained enough body fat to maintain its own body temperature. The placenta will also begin to provide antibodies to help boost the immune system. At full term, the baby should be around 7.5 pounds, although some will weigh more and others less.
