Between the first two to eight weeks the embryo begins to develop the major organs and the basic anatomy. Three distinct layers begin to develop and each form different parts. The outer layer forms the skin, hair, teeth, sense organs and the brain and spinal cord. The inner later produces the liver, pancreas and the digestive and respiratory system and the middle layer becomes the muscles, bones, blood and circulatory system.
Around the 5th week the nervous system begins to function by emitting weak brain waves.
Even as early as week 8, rudimentary eyes, nose and lips can be recognized and the embryo even has stubby bulges that will later become arms and legs
A 100,000 neurons are produced every minute during the second month of life and roughly half the fetus is what will be its head.
By around 12 weeks the fetus can swallow and urinate.
Also at 12 weeks the fetus’ arms will grow hands, which will grow fingers, which will grow nails.
At 16 weeks the baby can do somersaults, cry, hiccup, clench its fists, open and close its eyes and suck its thumb.
During the later half of pregnancy (near the third trimester) the baby urinates upto 1 liter a day. It also swallows the sterile fluid.
At the beginning of conception the uterus is the size of a pear and by the end of pregnancy the uterus is the size of a medium watermelon.