Baby Development: Weeks 1-12
Discover the amazing changes that happen each week as your baby grows and develops, from a tiny cluster of cells all the way to becoming a squalling newborn.
From a few gathered cells, an embryo has grown in seven weeks to a collection of developing blood vessels, vertebrae and internal organs (including a kidney that produces urine). The embryo is now half an inch long. The fingers are webbed and spread like starfish. Toes begin to sprout and feet take shape. Facial features organize as the retinas form, eyelids begin to develop, and the palate and ear canals begin to take shape. In males, the penis begins to form. In girls, the clitoris and the ovaries appear.
The embryo now measures 16 millimeters, about the size of a postage stamp. It looks more like a fetus, curled in the familiar fetal position and its legs are extended and arms have defined, bent elbows. The developing eyelids begin to close up, the external ears have begun to form, the nostrils are defined and open and the upper lip has begun to form.
The embryo measures 1.25 inches from crown to rump and weighs 1/30 of an ounce. Taste buds develop, the toes separate, and the intestines move out of the umbilical cord and fully into the embryo's body. All the organs are in place and distinctly formed. Now they must grow in size and become interconnected. As they do, the embryo becomes a fetus.
With all organs in place, your baby shifts its energy from developing into growing over the next seven months until it is a full-size, full-term infant. Tiny fingernails and toenails have begun to grow, and hair follicles develop below the surface of the skin. The head is large and round, and the neck is visible beneath the tucked head. In males, the penis bud is clear. In females, genitalia have begun to show.
Between 9 and 12 weeks, your baby doubles in size to three inches from head to toe. The connections between the nerves and the muscles have tripled since last week. Teeth begin to take shape. About 70 grams of amniotic fluid bathe your baby.
At the end of the first trimester, your baby weighs about 1/10 of an ounce. All of her major systems are in place, and all of her organs are formed and functioning. Now they begin the long, seven-month road to functioning outside the womb. Individuality is already present, as different babies have different facial expressions.