Pregnancy is divided into three phases, called trimesters. The first is zero to 12 weeks in duration; the second, 13 to 24, and the third, 25 to 40. According to Lucile Packard Children's Hospital at Stanford University, "The first trimester is the most fragile period, during which all major organs and systems are formed. Most birth defects and miscarriages occur during the first trimester. During the second and third trimester, the fetus is fully formed and grows and matures rapidly."
First Trimester
The most dramatic changes and development occur during the first trimester. After one month, the fertilized egg is 10,000 times larger than it was at conception. The baby is about 1-1/2 inches long after the second month, the heart is functioning, and the eyes, lips, tongue, ears are forming. By the third month, the baby is another inch longer and weighs about 1 ounce. Arms, hands, fingers, legs, feet and toes have developed, as have most of the organs and tissues. The eyes are almost completely formed. What was called an embryo for the first eight weeks is a fully formed fetus after 12.
Second Trimester
After four months the baby is 6-1/2 to 7 inches long and weighs between 6 and 7 oz. Increasing amounts of nourishment thickens the umbilical cord. Such reflexes as sucking and swallowing have developed, and soon to follow are rthe tooth buds and sweat glands. Toes and fingers have taken shape, and gender is apparent. By five months the baby is 8 to 10 inches long and weighs about a pound. The kin is pink and transparent. Eyebrows, eyelids and eyelashes are beginning to appear. Fetal movement is felt.
Third Trimester
At six months the baby is 11 to 14 inches long, weighs about 1-3/4 to 2 lbs, and begins to take its position head-down. Lungs are maturing. Eyelids open, taste buds form in the tongue, fat layers develop. Overall growth is swift, especially in the brain. By eight months the baby has grown another 4 to 5 inches and added another 2 to 4 lbs. Most organs are developed. Kidneys are mature. Kicks are felt. Movement can be seen. At the conclusion of the third trimester, the baby is about 19 to 21 inches long and weighs 6 to 9 lbs.
Birth Beckons
According to the website What To Expect, researchers theorize that the fetus sends chemical signals--or hormones-- to the placenta to initiate labor. "Other hormones are standing by, too," states the website. "During childbirth, your baby will produce more stress hormones than any other time in his or her life. But those hormones will actually help your baby adjust rapidly to life outside the womb and help all those survival instincts to kick in as he or she becomes untethered from the placenta that has provided life support for the past nine months."
Baby Overdue
According to What to Expect, "Fewer than 5 percent of babies are born on their actual due date--and around 50 percent decide to overstay thriving well into the tenth month. At birth, an overdue baby's skin likely will be temporarily dry, cracked, peeling, or wrinkled. This is because the protective vernix was shed weeks ago in anticipation of a delivery date that came and went. The baby will also have longer nails, possibly longer hair, and little or none of that baby fuzz--lanugo." The first breath of air will require considerable effort too: the tiny air sacs in the lungs need to be inflated for the first time--to breathe for a lifetime.
