Fetal Development From Weeks One to Eight

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By Misha Safranski
eHow Contributing Writer

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During the first 8 weeks following conception, an embryo transforms from a zygote to an embryo and finally into what is known as a fetus----a developing baby with all major bodily functions in place. Development of the fetus happens by leaps and bounds before a mother even knows she is pregnant. Fetal development from weeks one to eight is a miraculous physiological process that is now well understood thanks to modern technology.

Week One

From the first day of conception, the human zygote has a full set of 46 chromosomes, and gender is determined----XY chromosomes for a boy or XX for a girl. During the remainder of the first week, the embryo floats freely inside the uterus, the cells quickly dividing.

Week Two

During week two--typically between days 10 and 14 post-conception--the embryo settles into a spot within the uterus and the cells, which will become the placenta implant in the lining in order to transport nutrients from the mother's blood supply to the fetus.

Week Three

Week three in fetal development brings the formation of the middle layer of cells in the embryo. The heart begins to beat, and the neural tube forms; this will become the brain and spinal cord.

Weeks Four & FIve

In weeks four and five, the embryo begins to take shape with a head and tail-like structure. Eyes, mouth and limbs begin to form, complete with tiny finger and toe buds.

Week Six

Fetal development in the sixth week post-conception includes the growth of eyelids as well as significant brain development, making the head large in proportion to the rest of the embryo.

Weeks Seven & Eight

Weeks seven and eight of pregnancy reveal the development of ovaries or testes on the embryo, all major organs in place and the initiation of muscle movement. After the eighth week, the embryo has advanced to the fetal stage.