The period of embryonic development in side the womb or uterus starting from fertilization of to birth or parturition is called gestation of pregnancy .
The human gestation period being with the last menstrual cycle and end with the birth of child .
The pregnancy or gestation period lasts about 9 month or 40 week or 280 days . The gestation period is divided into 3 trimester , consisting of 3 month each .
FIRST TRIMESTER
It is consider 1st week to 13th week .
It is the initial period of development where the complex processes are being carried out .
These include the cleavage division , morula and blastula formation , gastrulation ,formation of notochord.
Then the organogenesis bring about formation of organs and organ system from the three germ layers i.e. ectoderm , mesoderm and endoderm .
Limbs of the embryo big in to develop as well as the gonads i.e. testis or ovary.
The baby heart begins to beat .
The nerves and muscles begin to work together . The make a first the eyelids close to protect the developing eye . They will not open again until week 28 .
At this time baby is about 7.5 C.M. long and weight almost 28 grams .
SECOND TRIMESTER
It is consider 14th week to 27th week.
Development of heart is improved or more and now it beats - 150 beats per minute .
The baby is more active . the mother might feel movement or kicking .
The eyes , nose , ears and face develop so that it begins to look like human .
The baby begins sucking motions with mouth .
Eye brows ,eye lashes ,fingernails and toenails have formed the baby can even scratch itself .
The babys bone marrow beings to make blood cells . The hairs begin to grow baby head . The baby weight about 680 grams and 30 C.M. long .
THIRD TRIMESTER
It is consider 28th week to birth .
Rapid growth of the foetus takes place . The baby is getting bigger and has less space to move around .The movement are less forceful but the mother will still feel them .
Final differentiation of tissues and organs takeplace
The development of the brain is advanced .
Grasp and suckling reflexes are apparent .
The baby bones are soft but fully formed . The eyes can open and close .
The baby organs are capable of functioning on their own .As the due date is near the baby may turn into a head down position for birth
The average birth weight is between 2.8K.G. to 4.1 K.G. and average length is 48 to 53 inches long .Most full term babies fall within these ranges but healthy babies come in many different and sizes .
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