In weeks 4 to 5 of early pregnancy, the embryo grows and develops within the lining of your womb. The outer cells reach out to form links with your blood supply. The inner cells form into 2, and then later into 3 layers. Each of these layers will grow to be different parts of your baby's body:
Your baby's nervous system is already developing, and the foundations for its major organs are in place. At this stage, the embryo is around 2mm long. The heart is forming as a simple tube-like structure. Your baby already has some of its own blood vessels and blood begins to circulate. A string of these blood vessels connects you to your baby and will become the umbilical cord. At the same time, the embryo's outer layer of cells develops a groove and folds to form a hollow tube called the neural tube. This will become your baby's brain and spinal cord.
By 7 weeks, the embryo has grown to about 10mm long from head to bottom. This measurement is called the crown-rump length. The brain is growing rapidly and this results in the head growing faster than the rest of the body. The embryo has a large forehead, and the eyes and ears continue to develop.
The inner ears start to develop, but the outer ears on the sides of the head will not appear for a couple more weeks. The limb buds start to form cartilage, which will develop into the bones of the legs and arms.
By the time you're 8 weeks pregnant, your baby is called a fetus, which means offspring. The legs are getting longer. The different parts of the leg are not properly distinct yet. It'll be a bit longer before the knees, ankles, thighs and toes develop. The fetus is still inside its amniotic sac and the placenta is continuing to develop, forming structures that help attach the placenta to the wall of the womb.
Your baby's face is slowly forming. The eyes are bigger and more obvious and have some colour (pigment) in them. There's a mouth and a tongue with tiny taste buds. The hands and feet are developing – ridges identify where the fingers and toes will be, although they have not separated out yet. The major internal organs, such as the heart, brain, lungs, kidneys and gut, continue developing. At 9 weeks of pregnancy, your baby has grown to about 22mm long from head to bottom.
The ears are starting to develop on the sides of your baby's head, and the ear canals are forming inside the head. If you could look at your baby's face, you'd be able to see an upper lip and 2 tiny nostrils in the nose. The jawbones are developing and already contain all the future milk teeth. The heart is now fully formed. It beats 180 times a minute – that's 2 to 3 times faster than your own heart.
Just 12 weeks after your last period, the fetus is fully formed. All the organs, muscles, limbs and bones are in place, and the sex organs are well developed. From now on, the baby has to grow and mature. It's too early for you to be able to feel the baby's movements yet, although they'll be moving quite a bit.
