Pregnancy- Embryonic and Fetal Development

Page by Bri Hearn and Dan Friedman




Human Fetus

Study Guide

Summary: Embryonic and Fetal Development

Before a baby is born, it goes through three steps of prenatal development: fertilization, the embryonic period, and the fetal period. During fertilization, many sperm cells fuse with an egg cell, forming the zygote. This zygote will divide a few times before it is classified as a blastocyst, or small collection of developing cells.
By about the third week of pregnancy, the embryonic period begins. At the very start of the period, the embryo goes through many steps of basic growth where the brain, spinal chord, and digestive tract gradually appear. The next five weeks are a time for the embryo to develop most of the basic body parts and to evolve into a fetus.
By the approximately the ninth week of pregnancy, the baby enters the fetal period. The fetal period is the last and longest stage of pregnancy, and the baby goes through its most intense development during this time. Over the course of the first eight or nine weeks of this stage, the baby rapidly increases in size from about three inches to around ten inches in length. The fetus also begins to grow thin hair during this time called lanugo. After the development of these and other features, the fetus has reached its 24th week, and it would be able to survive on its own with the help of medical technology. The following fourteen or sixteen weeks include rapid growth and disappearance of the lanugo for the fetus, and by the 38th week, it is considered ready to be delivered. At this time, the baby could be up to twenty inches and ten pounds.

Key Vocabulary:



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Multiple Choice Test:

Human Embryo

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