By this week your fertilised egg has embedded into the delicate lining of your uterus and the mass of cells which will eventually become your baby continue to divide and multiply. Even though miraculous events are taking place and a life is starting to form, your baby is still only about 1mm. Week four of pregnancy is usually regarded as the beginning of the embryonic period as your baby’s major organs and spine will all start to develop from now on. This means absolutely no alcohol or smoking as both can cause damage to the foetus. The placenta, which when fully grown will become your baby’s life support system, will start to form from now onwards but it will be a few months before your baby comes to rely on it.