Fetal Development

Week 1: Conception; the baby is smaller than a grain of sugar, but the instructions are present for all that this person will ever become.

Week 2: The baby attached and burrows securely into the wall of its mother’s womb.

Week 3: The baby’s blood vessels and sex cells form, Foundations of the brain, spinal cord and nervous system are laid.

Week 4: The baby’s heart has begun to beat. Eyes, ears and lungs begin to form.

Week 5: Tiny arms and legs appear, as well as the baby’s face. The baby’s blood is now separate from the mother’s blood.

Week 6: Tiny fingers and toes develop. The baby’s brain is divided into 3 parts for emotion and language, hearing, and seeing.

Week 7: Buds of the baby’s milk teeth appear. 99% of the muscles are present, and brain activity is detectable.

Week 8: The baby begins spontaneous movement and is now well proportioned, about the size of a thumb. Every organ is present, but immature. The skull, elbows, and knees are forming.

Week 9: If prodded, hands and eyelids close. Genitalia becomes visible, indicating whether the baby is a boy or a girl. Muscular movement begins.

Week 10: The baby’s fingerprints begin to form. Nerve and muscle connections have tripled. Eyelids fuse together temporarily to protect the baby’s delicate developing eyes.

Week 11: The baby “practices” breathing and facial expressions, even smiling. The baby can also urinate, and stomach muscles can contract.

Week 12: The baby is now 3 inches in length and weighs 2 oz. with fine hair on the face. The baby is able to swallow and feels and responds to skin stimulation.

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Medical fact sources: Carlson, B., Human Embryology & Developmental Biology, Toronto: Mosby Publication; 3rd edition, 2004. Moore, K. and Persaud, T., The Developing Human, Clinically Oriented Embryology, 6th Edition, Philadelphia: W.B. Sanders, 1998. O’Rahilly, R. and Muller, F., Human Embryology and Teratology, 3rd Edition, New York: John Wiley and Sons, Inc, 2001. Hadlock FP, Shah YP, Kanon DJ, et al. “Fetal crown rump length: Reevaluation of relation to menstrual age with high resolution real-time US Radiology.” 182:501, 1992.