What is the embryonic period of the 1st trimester of pregnancy?

The third week of pregnancy is usually when your egg is fertilized and your child conceived. After the egg implants in the uterine wall, it remain in an embryonic period from the fifth to the tenth week. This is when most of your baby's organs develop. Your child is a around the size of a sesame seed at week 5, but grows to over an inch long by week ten. The embryonic stage is the most important stage of development because it sets the precedent for the rest of your child's growth and health.

Following fertilization the rapidly growing mass of cells, attaches to the uterine wall and forms layers of cells called the embryo. This is the beginning of the embryonic period which occurs between 2 and 8 weeks after conception. This is a time of rapid cell division, movement and differentiation. The inner layer of cells of the embryo is the endoderm which develops into the digestive and respiratory systems, the middle layer of cells or mesoderm develops into the circulatory system, bones, muscles, excretory system and reproductive system and the outer layer of cells or ectoderm becomes the nervous system and sensory receptors. During the embryonic period most of the organ systems are established thus during this period of pregnancy the embryo is very vulnerable and many anomalies are produced during this time.

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