Over a period of 40 weeks, a baby starts life as a single cell and rapidly develops into a distinguishable human being with his own characteristics. Starting with a basic human-like shape, cells continue to develop features and survival systems that will allow your baby to enter the world prepared for life outside the womb.
Zygote
Both a sperm and an egg contain 23 chromosomes. When a woman's egg is penetrated by a sperm, a new living cell is created called a zygote, which contains 46 chromosomes. According to "The Developing Person," within hours of conception the zygote will divide and rapidly begin duplicating exact copies of itself. The bundle of cells reaches the uterus and develops into a fetus and placenta.
First Trimester
During the first two months, although the head and facial features are taking shape, you would be unable to recognize your baby as a human being. According to "What to Expect When You're Expecting," during the first month, your baby is smaller than a grain of rice and appears to have a tail where the lower portion of the spinal cord is developing. The cardiovascular system is the first to show activity, which you will discover when you and the doctor listen to the baby's heartbeat.
By the end of the second month, your baby looks more human-like. According to the American Pregnancy Association, everything present in an adult is now in the embryo.
As the first trimester comes to an end, the genitals are fully formed, and the baby now has taste buds and buds for baby teeth to emerge.
Second Trimester
The second trimester begins at 14 weeks. According to "What to Expect When You're Expecting," your baby can now suck his thumb, which shows the development of motor skills and the suckling reflex that will allow your baby to nurse.
The second trimester is an active time for your baby. You may feel kicks around the fifth month. In addition to kicks, you may be feeling your baby do full somersaults. According to "What to Expect When You're Expecting," the ears have developed, so your baby can begin hearing sounds.
According to "The Developing Person," babies born before 22 weeks are unable to survive since the brain is incapable of basic functions. However, many babies are able to survive with life support a few weeks later.
By the end of the second trimester, your baby is around 14 to 17 inches and weighs around 4 ½ lbs, according to the American Pregnancy Association.
Third Trimester
Approximately 33 weeks into your pregnancy, your baby moves so the head is downward to prepare for delivery. During your baby's last month in the womb, she becomes less wrinkled and appears plump as she rapidly gains weight. According to the American Congress of Obstetricians and Gynecologists, babies gain an average of 1/2 lb. per week during the ninth month of development in the womb.
Although immature, the lungs begin to function this trimester, taking in amniotic fluid.
Newborn
According to "The Developing Person," your baby is a bluish color at birth; however, her color improves as oxygen circulates between cries. A normal baby weighs 5 ½ to 9 lbs.
A healthy baby is pink and has a heartbeat over 100. In addition, she has reflexes, such as coughing, sneezing and crying. According to "The Developing Person," newborns can step forward when held upright.
References
- "The Developing Person: Through the Life Span"; Kathleen Stassen Berger; 2008
- "What to Expect When You're Expecting"; Heidi Murkoff, Arlene Eisenberg, & Sandee Hathaway; 2002
- American Pregnancy Association: Fetal Development
