From the moment of conception, the minute cluster of cells that is a baby, starts to develop rapidly into a fully formed human being. A baby takes all the nourishment from the mother in order to bring about the miracle of a new life. In the first 12 weeks of life, a baby changes rapidly from an indistinct bundle of cells into an identifiable human form. During this time, the body starts to form and all the major organs are developing.
By eight weeks, the four chambers of of the heart have formed and it can be seen beating on an ultrasound. At this stage the baby can be called a “fetus”. The baby, now called a fetus, loses its tail and limbs and starts the process of forming a body.
By 12 weeks, the end of the first tri-mester, your baby is fully formed; facial features are developing and the major organs are beginning to function. The second tri-mester, from weeks 13-27 weeks, is a period of rapid growth as a baby grows from 2 in (6cm) each month. This is when a baby starts to move and can swallow and hear sounds outside the womb.
By 24 weeks, most body systems are formed and, except for the lungs, the major organs are all working. By the third tri-mester a baby is now much more in proportion. A greasy protective substance called vernix covers the skin. By the third tri-mester, at 28 weeks, a baby has put on considerable weight and and if born can possibly survive outside the womb with the proper medical care. During the last tri-mester, a baby becomes much more active and and is likely to have some sort of sleeping and waking routine. The baby may also start to fill out and resemble a newborn as fat deposits are laid down. The organs continue to mature and the body systems are becoming more and more complex. The brain and nervous system develop rapidly and the brain will still continue to develop in a baby after birth.
By 36 weeks, the liver and kidneys are fully developed and the liver is starting to process waste products. The digestive system has formed and the intestines are filled with meconium, a dark green substance made of waste products. The lungs are among the last organs to fully develop, but by only 40 weeks these are fully functioning and a baby starts to practice small breaths.