The journey through a pregnancy is a thrilling, scary, emotional ride. For nine months, you will have another human being growing inside of you--one that you helped to create. While you're busy readying your family for its newest member, shopping for a layette and painting the nursery, your baby is going through a world of changes as it prepares for life outside the womb.
The Early Days
Technically, pregnancy begins when a man's sperm joins with a woman's egg, up to two weeks before you even suspect you are pregnant. In the days following conception, the fetus's neural tube, which will develop into the nervous system, begins to form. At this very early stage, your baby already has the foundation for thought, senses and feeling. Also in these first days, the heart and primitive circulatory system quickly form. Though still in the beginning stages, this is the support system that will carry your child throughout his life.
First Trimester
During the first eight weeks of pregnancy, a fetus is called an embryo. The embryo develops very quickly, and by the end of the first trimester, it weighs about 1/2 to 1 oz. and measures approximately 3 to 4 inches in length. By the end of eight weeks, the embryo has taken on a human shape, and the eyes, nose, mouth and ears become more distinct. The arms, legs, fingers and toes are clearly visible, though the fingers and toes are still webbed. The baby's major organs develop quickly and its heartbeat can be heard using a Doppler. Though the mother cannot yet feel movement, the embryo is constantly in motion. By the end of the first trimester (12 weeks gestation), the eyelids, fingernails and toenails are formed, and the external genital organs are developed.
Second Trimester
By the end of the first trimester, all of the baby's major organs are formed. For the rest of the pregnancy, they will continue to grow and develop. By the end of the second trimester, about 28 weeks gestation, the fetus will be approximately 13 to 16 inches long and weigh 2 to 3 pounds. During this trimester, the fetus learns to suck and swallow and will respond to certain stimuli. Fat and hair begin to develop and grow, and the skin becomes wrinkly and red, covered with soft, downy hair called lanugo. The baby's eyelids begin to open, and eyebrows and eyelashes become visible.
Third Trimester
By the time the baby reaches the third trimester, about 28 weeks gestation, all major systems have developed, and the baby stands a good chance of surviving if born prematurely. The baby's brain will continue to develop, and the lungs start taking "practice" breaths. The baby does not have as much room to turn somersaults anymore, and her knees will be tucked to her chest in "fetal" position. She will also start moving into birth position, somewhere around 36 weeks. She continues grow through the last trimester, until she day she is born. Most full-term babies weigh somewhere between 6 pounds, 2 ounces, and 9 pounds, 2 ounces. The average length of a newborn ranges from 19 to 21 inches.
Warning
Good prenatal care is essential to the health of you and your baby. Be sure to visit your doctor regularly to ensure that you and the baby are getting the care you need for a healthy pregnancy and delivery.
