God has made every living thing in pairs. When the sperm from the male and egg from the female unite, an earliest form of life comes into being that is embryo.

During the life cycle of child's development, male's sperm and female's egg fertilize and form a structure that is called as zygote. Zygote is the most initial structure in the process of child's development. Cells in the zygote divide by the mitotic division and get double in number that is two cells divide into four and four cells divide into eight daughter cells and the process goes on. When so many cells are produced, they start differentiating and adopt different properties and functions.

An embryo is an organism during the early stages of development. The branch of science which deals with the study of embryo is called as embryology. Embryo starts developing when the egg is fertilized and cells start multiplying at the zygotic level. The zygote turns into an embryo. It is not able to survive on its own but needs food and other necessary components from the other source that is usually the mother.

Stages of Development:-
An embryo undergoes following stages of development to become a complete independent organism.

First Month:-
In the first week of child's development, the ovum stays in the uterine tube. It becomes fertilized at the upper part of the uterine tube. From that point, slowly it moves down and reaches into the uterus. During this period, the ovum keeps multiplying and undergoes segmentation. The process is called implantation.

During the sexual intercourse, many sperm enter the woman, but there is only one which succeeded to enter the egg. A sperm is a tadpole like structure. When it enters the egg, it leaves its tail outside and the other part enters the egg. The tail contains the mitochondria. So when it enters the egg, mitochondrion is left outside. When a child develops, all the cells of the body have the mitochondria from the mother. After sperm's entry into the egg, the egg wall toughens up stopping other sperm to enter the egg. A child gets half of the DNA from his father and half part from his mother.

When egg reaches the uterus, it attaches itself to the uterus wall. Now it has gotten the shape of a little ball. The cells outside the ball develop into placenta and cells present inside the ball become the baby. After the woman conceives, a hormone is released from her body called progesterone, which tells the woman that now she will not have periods until the nine months.

Second Month:-
Now the fertilized egg or little ball is called as the embryo. It is of very small size and its cells are distinguished in three different layers. Brain and nerves and other simple things like hair and tooth enamel are produced by the first layer. Middle layer is involved in the formation of bones, muscles and blood vessels. Heart and some parts of the lungs are also formed by this layer. Urinary tract, kidneys, intestines and other parts of the lungs are developed by the inner layer. A place is formed at each end of the embryo, one near the heart and lungs will be the head and the other will develop into anus.

When the embryo reaches sixth week, small bumps will start producing. They will develop into arms and legs in the later stages. Stomach and lungs will take their places. The heart's parts which wee formed separately now fuse together and start beating. At this stage, the umbilical cord is formed in the body which is attached to the uterus from one end and to the body from other end. It will be the source of providing nourishment to the child. Now the embryo looks like a human body. Baby's eyes start emerging from the brain but they will still be at the side of the brain. Hands start developing into fingers.

Third Month:-
Though not mature but now the child has all the internal organs. Ovaries produce in the girls and testes in the boys at this stage. But doctors still cannot predict what the sex of the child is. In ninth week, the umbilical cord develops fully containing one large vein and one large artery. The embryo is no more an embryo now but it develops into a fetus. Eyelids form on the eyes and eyes take their actual position in front of the brain. Now baby looks like a human. The eyes are closed yet.

Fourth Month:-
At this level, woman starts showing the sign that she is pregnant because her tummy takes the shape of a bump. Finger nails start producing and gallbladder makes bile at this stage. This stage completely shows the sex organs of the child and a couple can know about the sex of their child. The hair begin to grow on the head, eyelashes and eye brows. Hair also produces on overall body of the child in swirling manner but they disappear shortly after birth. At this stage woman does not have any fear of miscarriage. The amniotic fluid surrounds the fetus. This fluid is removed when the child swallows it but it does not harm the child's body. Fetus becomes 5 inches long at this stage.

Fifth Month:-
At this stage, baby starts kicking the mother and starts exploring the world he is living in. the number of the nerve cells grow rapidly in the brain. Baby starts hearing the sounds of the surrounding environment like sound of blood vessels. It is an unbelievable fact that if the child is a girl, it will start producing its own eggs which after many years will undergo the same process. First stool forms in the child which is called as meconium. Baby's skin will be covered up with a yellow substance called vernix. The hair or lanugo will protect the body from amniotic fluids and keep it at its place. The baby is now 7 inches long.

Sixth Month:-
Bones get hardened at this stage as well as child gains weight and other can also see that baby is moving. It can also hear the noises of the outside world. His lungs are developed fully now and they are ready to take breath. The eyes are still closed.

Seventh Month:-
At this stage, the baby's legs are fully formed and it can now change its position. A mother can feel herself that child is changing positions. Baby's eyelids completely developed and baby gets its eyesight. Now he is not only able to see but also can hear. The bran rapidly develops and takes its shape in the form of wrinkles. Each part of the brain knows its duty that is speech, hearing, seeing etc. if the child is a boy, hs testicle will move to its original place.

Eighth Month:-
Now the baby is fully developed and waiting for his departure from the womb. Many antibodies enter the child's body from mother's immune system so that he does not get any infections after birth. Breastfeeding can make child's immune system stronger.

Ninth Month:-
At this stage the baby is fully developed and ready to come out. In some cases, child is born through normal way but if there are some complications regarding the birth of the child then doctors do caesarian.

A child completes the woman and she feels very happy after having a child.

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