In the first 3 months, your baby is called an embryo (EM-bree-oh). That is the Greek word for “to grow.” The embryo is so small you wouldn’t be able to see it with the naked eye. But the baby is very busy. During the first weeks, the embryo travels from the fallopian tube to the womb, or uterus. The outer cells of the embryo burrow into the wall of the uterus to create the placenta, which will nourish baby.
The inner cell groups divide into 3 layers that will grow to become the lungs, stomach, heart, kidneys, spinal cord, face, and skin. All of this happens before you have even missed a period. By the end of the first month, your baby is a tiny, tadpole-like embryo, smaller than a grain of rice.
Early in the second month, baby’s brain, spinal cord, heart, digestive tract, sense organs (such as eyes and ears), and arm and leg buds begin to form. The embryo grows like a soap bubble, swelling from the inside and becoming longer. The outer layer of cells grows to become the baby’s skin and nerves. The middle layer grows to become bones, muscles, blood vessels, kidneys, and sex organs. The inner layer grows into the lungs and digestive system.
Your baby is moving, although it is still too small for you to feel. Its eyelids are closed. The inner ear is formed, and the outer ear is developing. The baby’s sex organs are beginning to form.
The placenta and umbilical cord are working to give baby what it needs and to take away its wastes. By the 10th week, the baby is called a fetus (FEE-tis). It is about an inch and a half long and weighs about as much as a letter you receive in the mail. At the end of 12 weeks, baby is bending and stretching its legs, opening and closing its fists, and nodding its head. Tooth buds and taste buds are forming.
By the end of the fourth month, the 4-inch baby is developing reflexes, such as sucking and swallowing. Its body begins to grow faster than its head. Tooth buds appear. Fingers and toes are becoming well defined.
By the end of the fifth month, you will begin to feel the 8-inch to 10-inch baby moving. Soft, fine hair called lanugo (la-NOO-go) covers its body. Hair begins to grow on its head and eyebrows. The baby’s white eyelashes appear. A protective coating called vernix, a cream cheese-like substance, covers the baby.
The baby is about 13 inches long and weighs about 1 3/4 pounds. Its skin is thin and shiny with no fat underneath. Baby’s fingerprints and toe prints can be seen. The baby can open its eyes. If the baby were born now, it might survive with intensive care.
Your baby is beginning to develop fat tissue. Baby may suck its thumb, hiccup, or cry. He or she now can taste sweet and sour. The baby responds to pain, light, and sound. The baby weighs about 3 pounds and fills your womb.
Your baby is about 18 inches long and weighs 5 pounds. Its brain is growing quickly now. Baby can see and hear. Most of its organs and systems are well developed. Its lungs may still be immature.
Final preparations are being made for baby’s birth, which can take place any time now. Babies often have less room to move around, but you should not notice less activity. If you do notice that baby is moving less, call your doctor right away. Baby’s lungs are probably mature. This month, baby will grow about 2 inches and 2 1/2 pounds. At birth, the average baby weighs 7 1/2 pounds and is 20 inches long.