Pregnancy Education - Development of the Embryo and Fetus First Trimester Week 2 – Conception occurs when the sperm penetrates the ovum. The fertilized cell is called a zygote and is smaller than a grain of salt. It contains 23 chromosomes from each parent, resulting in a complex genetic makeup for every feature of human development – the child’s sex, hair color, eye color, height and skin tone. Week 4 – The embryo may float in the uterus for about 48 hours before implanting itself in the lining of the uterus. The placenta forms.
Week 10 – The embryo is now about 1-inch long. Cartilage, bones, joints, facial features, limbs, hands, feet, fingers and toes are taking shape. The nervous system is responsive, and several internal organs have started to function. The fetus even has fingerprints. Week 14 – The 3-inch long fetus weighs about an ounce. Muscles are developing, and movement can be observed. Over the past few weeks, sex organs, hair and eyelids have been forming. The fetus is producing hormones and may be able to suck his thumb. Second Trimester
Week 22 – At nearly a pound, the fetus now has skin that has changed from transparent to opaque. Nerve cells for the senses have been developing. The fetus can hear noises outside of the womb. Week 26 – The fetus’ eyes are fully developed and can blink, and taste buds have started to form. Sweat glands have been developing, and spine structures have begun to form. The fetus can breathe and cry, and has a more than 50% chance of living outside of the womb. Third Trimester
Week 36 – The baby’s five senses are intact. She can blink and has fully developed kidneys. Week 40 – The child has a firm grasp, has grown significantly, and is now prepared for life outside of the womb.
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