The period of development that includes the creation of the zygote, attachment to the uterine wall, and continued cell division is known as the gestation period.

The gestation period for humans is normally 9 months. The spermatozoa fuse with the ovum to form a single-celled zygote in the ampullary region of the fallopian tube.

The germinal period is initiated with germinal stage and is followed by embryonic period.

Germinal period:

The fusion of spermatozoa with the ovum to form a zygote is called fertilization. The zygote then follows mitotic division and increases in cell numbers in the route of 2, 4, 16, 32… and so on. These series of divisions are known as cleavages. The embryo of up to 32 cells is called a morula. As more cleavages take place, the morula turns into a hollow ball of cells called a blastula. The blastula is enclosed in a protective sheath called a blastocyst. The blastula gets embedded into the endometrial lining of the uterus. This is called implantation. The blastocyst develops the placenta. The placenta supplies the essential nutrients required for the development of the embryo.

Embryonic period:

The embryo is connected to the placenta through the means of an umbilical cord. The transmission of nutrients to the embryo from the placenta occurs through the umbilical cord. When the embryo is developed it is called a fetus. The fetus remains generally in a head-down position toward the cervix through which it is transferred out from the uterus. This procedure of expelling the fetus out of the mother's body is commonly known as delivery.

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