A baby. A five day old embryo that has already developed from one cell (called a zygote) into a morula (12-16 cells) into a blastocyst (40-150 cells). In five days the baby grows from 1 cell to over 100. Incredible. And all of these cells will turn into the different kinds of cells that are in our body. That's one reason why scientists want to do research on embryos. They can't figure out how one cell can create everything in the human body. They want to be able to do the same thing that this tiny embryo does. It is like tearing open a rose bud so that you can find out what makes it blossom. Only the rose bud isn't made in the image of God.
This is what a blastocyst looks like.
From the moment of conception this baby has a sex, eye color, hair color, and skin color. Depending on what researchers you listen to, its personality, height, weight, and intelligence are also there, encoded right into that DNA. From the moment the sperm enters the egg a unique person with his or her own unique set of genetic traits has been formed. In five days, the baby is in the blastocyst stage and is moving out of the Fallopian tube in preparation to implant in the uterine wall. The baby now has a ring of cells surrounding it that will become the placenta and umbilical cord (these cells are called the trophoblast) and the cells of the baby itself are called the embryoblast. All of this has a protective covering called the zona pellucida that protects the baby from the uterine environment until it is developed enough to implant. The baby breaks out of this "shell" around the sixth day after conception. There is a complex chemical process that occurs between baby and mother that allows the embryo to implant. The mother's uterine wall (called the endometrium, just in case you wanted to know--:)--) actually partially absorbs the baby and begins rerouting capillaries to nourish the baby. Here is a photo of a baby nestled snugly in the endometrium:
The speed of development is amazing. I won't bore everyone with a long(er) post about every step of fetal development, but suffice it to say that 23 days after conception a tiny immature heart begins to beat, and by day 28 arms, legs, and eyes have begun to develop. This is all before most women know that they are pregnant. Here is a five week old embie:
By the eighth week the baby is more than 1 inch long and all of its organs and systems are present. All they need to do is grow and mature. This why doctors caution women to be extremely careful with nutrition and what they expose themselves to in early pregnancy. Since all of these vital organs and systems are forming, this is the time that the baby is the most fragile and vulnerable. Every conception website will tell you to be especially careful to get complete nutrition and vitamins and to avoid harmful substances if you want to conceive.
For some more embryo development info, you can check out these sites:
For Biology Info: