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The first trimester of pregnancy constitutes the first 12 weeks and can be a precarious time as your pregnancy becomes established in your body. Knowing how your baby is developing and growing important organs can shed some light on how you deal with your body to best nurture the new life inside you.
The most profound and dramatic development of your baby takes place in the first trimester. This is the time when the fertilized egg makes the trip down the Fallopian tube to implant in the wall of your uterus. Once that happens, powerful hormones kick into place to sustain your pregnancy while your body continues to treat it like a foreign invader. That is the reason for some miscarriages, since the body does not always produce the appropriate amount of hormones.
During the first week after fertilization, the pregnancy becomes established and the embryo begins to grow and develop. During the second week, groups of rapidly growing cells in the embryo are preparing to become various organs and body systems. During week three, the brain and heart start developing as do a primitive circulation system.
By the fourth week, the embryo has a head and a tail and does not look much like a baby at all. Not to worry though, for it will certainly become a baby-looking fetus before too long. The beginning of the eyes and ears are starting to take shape while the heart beats away providing life to the growing human being. Even though the embryo is less than one-half inch long, all the necessary organs have begun forming.
Into the fifth week of pregnancy, the lungs have become tiny organs on both sides of the abdominal cavity. Both the kidney and liver have started to take shape as do the arms and legs which begin as tiny buds. The eyes will now be visible as will indentations where the nostrils will be.
Between four and six weeks, the placenta takes over the task of supplying the hormones necessary for pregnancy, giving a break to the ovary's formed corpus luteum which had been supplying hormones up until that point.
At six weeks, the stomach can be seen and recognized and the tail still observable but no longer growing. The face now undergoes dramatic changes which liken the embryo more to a human and less to a tadpole. Eyes and nostrils are distinct and all internal organs are done forming. The heart continues to beat strongly and the circulatory system is complete. Hands and feet will be formed by the seventh week and the tail will disappear. At two months, eight weeks, the nose and upper jaw will grow rapidly and conditions like cleft palate will occur now.
Once the eighth week has arrived, the embryo becomes a fetus in terms of medical identification. The head remains bigger than the body in comparison and fingers and toes are still webbed.
During the third month which are weeks nine through twelve, external genitals appear though gender could not yet be determined by ultrasound. The fetus's digestive tract also becomes formed though there will be nothing to digest until after birth. Once twelve weeks have passed, the limbs and internal organs are fully formed. Thus is the reason for being cautious about medications during the first trimester since that is when your baby is doing the most crucial developing.
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