How a Fetus Grows
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Stages of Fetal Development
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The development of a baby from conception to birth can be divided into three stages: germinal, embryonic and fetal.
The germinal stage of fetal development lasts about two weeks. It occurs from the time of fertilization until implantation in the uterine wall. Next comes the embryonic stage of fetal development, which lasts about eight weeks. Major body structures--like heart, brain, liver and sex organs--are formed. The baby's heart is beating by seven weeks. This time is the most critical in fetal development, where the embryo is very vulnerable to damage.
From week eight until birth around week 40, the baby is called a fetus. Its major task is to grow. In this time, all body systems begin to function.
First Trimester: Months 1, 2 and 3
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The first stage of pregnancy is the time the zygote implants itself in the uterus lining. Rapid cell division takes place there, and organs--such as the spinal cord and heart--begin to form.
In the second month of pregnancy, the head area develops rather quickly; the nose, eyes and eyelids are forming. Also, internal organs are growing. Arms and legs grow and can be clearly distinguished. Every organ is in place.
Eyes are directed forward towards the end of the first trimester. The baby also develops taste buds on its tongue. Most organs have structurally developed by this time; hands, arms, legs and toes have developed as well.
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Second Trimester: Months 4, 5 and 6
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Month four is eagerly awaited by many parents; it's at this stage that the sex organs of the fetus become distinctly visible by ultrasound. Now, the fetus floats around and exhibits reflexes like swallowing. In the next month, the baby's fine lanugo hair starts growing. Also, it might be the first time that the expecting mother can feel her son or daughter move. Organs continue to mature, but they are still quite immature at this time. The fetus can be seen thumb-sucking on the ultrasound; it has hiccups and kicks vigorously.
Eye movement (opening and closing) begins around the end of the second trimester. The baby continues to grow at a fast speed.
Third Trimester: Months 7, 8 and 9
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In month seven, the baby might respond to loud noises. With fat deposits developing under the skin, it becomes less transparent. All organs except for the lungs are fully mature at this time. For the mother, it is more noticeable when her baby is awake or is sleeping.
The fetus goes through another grows spur as the pregnancy nears its end. To prepare for birth, the baby will begin its downward move into the mother's pelvis. Lungs are matured, and all organs are completely functioning. Head down, the baby is in a "ready" position. He's ready to be welcomed into the world.
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References
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