Define fetus and stages of Fetus for 20 Weeks and above

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A developing mammal or fetus is usually in the later stages of pregnancy. The unborn young of a viviparous vertebrate is called an embryo until at least 8 weeks after fertilization; after which it is called a fetus. A medical term for a newborn or very young child (birth to 1 year). It is anybody’s system that develops from the embryonic stage and continues through the fetal stage where you can see all major organ systems and parts including brain, heart, eyes, etc. Fetus means “little one” in Latin and we use this term because humans (and other

Here are some of the stages of fetus growth:


A snow covered street

This is the process in which male gametes, spermatozoon, fuse with a female gamete, the oocyte, to form a single cell called a zygote. At this moment of fertilization, an embryo begins to develop. The fusion of male and female sex cells or the combination of 23 chromosomes from the mother and 23 chromosomes from the father results in 46 chromosomes. This complete set determines all genetic traits of the fetus.


This occurs at about 6 days after fertilization while the zygote starts traveling down the fallopian tube towards the uterus where it will implant itself into the uterine wall for further growth under the protection of the maternal organism. Zygote implants itself into the endometrium lining completely and begins to form embryoblast which later turns into a blastocyst. This stage ensures further growth and development of the embryo.

Embryonic Stage

The embryo continues its growth under the protection of maternal organisms till it reaches a size of about 0.1 inches or 3 millimeters. The main features of the embryonic stage are rapid cell division and differentiating tissues, organs, and organ systems from each other.


Organogenesis begins towards the end of the embryonic stage at around the 7th week when all organs begin developing in the fetus with the head facing downwards while supported by amniotic fluid inside the amniotic sac-filled uterus. This process continues till birth while the fetus remains completely reliant on the placenta for nutrition, waste removal, and gas exchange till the 14th week.

Fetus Growth prenatal

At this stage, the fetus measures about 1 inch or 25 millimeters with rapid growth in all aspects of its development. It weighs around 0.1 ounces at 10 weeks and 0.45 ounces at 20 weeks.


By the end of pregnancy, the cervix is completely effaced, dilated to 10cm diameter while the head of the baby is engaged in the pelvis facing downwards so that it can descend through the vaginal canal for exit from the maternal organism and independent life.


By the end of this stage, the fetus is completely developed to be born as a separate being. All organs have reached their full growth and functional development by birth with a complete tandem of physical, chemical, immune, and hormonal systems to support life outside the mother.

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