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Your Developing Baby, Week by Week

Your baby begins as a tiny cluster of cells, but during the nine-month process of pregnancy she becomes an amazing baby with facial features, a beating heart and kicking legs. Find out what's happening with baby's development week by week.
week 5 Week 5

This week, your baby's ticker will start beating for the first time! (Neither you nor your doctor can hear it yet, but it may be possible to see the movement on an ultrasound.) And your little one has been really busy growing! The embryo now has three distinct layers: the outer ectoderm, which will form the nervous system, ears, eyes, inner ear and many connective tissues; the endoderm, or inner layer, which will grow into internal organs like the lungs, intestines and bladder; and the middle mesoderm, which will eventually make way for the heart and circulatory system. In the weeks to come, the mesoderm will also evolve into bones, muscles, kidneys and reproductive organs.