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Pre-embryonic Development
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1 week
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Ovulation Occurs
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Fertilization occurs, cell division begins and continues, chorion appears
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Embryonic Development
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2 weeks
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Symptoms of early pregnancy (nausea, breast swelling and tenderness, fatigue); blood pregnancy tests may show positive
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Implantation occurs; amnion and yolk sac appear; embryo has tissue; placenta begins to form
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3 weeks
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First period missed; urine pregnancy test may show positive; early pregnancy symptoms continue
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Nervous system begins to develop; allantois and blood vessels are present and placenta is well formed
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4 weeks
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Limb buds form; heart is beating; nervous system further develops; embryo has tail; other systems are forming
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5 weeks
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Uterus is the size of a hen's egg; mother may need to urinate frequently
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Embryo is curved, head is large, limb buds are showing division, nose, ears and eyes are noticeable
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6 weeks
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Uterus is the size of an orange
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Fingers and toes are present and skeleton is cartilaginous
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8 weeks
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Uterus can be felt above the pubic bone
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Fetus begins to look human; limbs are developing and major organs forming; facial features are becoming refined
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Fetal Development
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12 weeks
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Uterus is the size of a grapefruit
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Head grows faster than the rest of the body; facial features are apparent, but there is no layer of fat yet and the skin is translucent; gender can be distinguished via ultrasound; fingernails appear
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16 weeks
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Fetal movement can be felt
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Fine hair (lanugo) grows over the body; fetus resembles a tiny human being; skeleton is visible
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20-22 weeks
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Uterus reaches up to the level of umbilicus and pregnancy is obvious
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Vernix caseosa, the protective fatty coating, begins to be deposited; heartbeat can be heard
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24 weeks
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Doctor can tell where baby's head, back and limbs are; breasts have enlarged and nipples and areola are darker, colostrum is produced
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Fully formed but still thin; much larger and very active, all major organs are working, the lungs and digestive system need more time to develop; body is covered in fine hair called lanugo
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32 weeks
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Uterus reaches halfway between umbilicus and rib cage
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Most babies are in a head down position in the womb; head is more in proportion to the body; eyes are open; babies born at this stage have a good chance of living
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36 weeks
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Weight gain is averaging about a pound a week; standing and walking are becoming very difficult because the center of gravity is thrown forward
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Body hair begins to disappear, fat is being deposited
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40 weeks
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Uterus is up to the rib cage, causing shortness of breath and heartburn; sleeping is very difficult
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Not much room to move in the womb; fully mature, baby
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