Embryo - Pregnancy Stages

Your developing baby will go through many changes and pregnancy stages from conception until the day he is born. During the first couple of months in the pregnancy calendar, your baby is in the embryonic stage. Then he will grow into the fetus stage and will remain a fetus until the day he is born.


The human embryo starts off as fertilized egg called a zygote. The egg is fertilized when it is released during ovulation and is fertilized by the sperm in a process called conception. Traditionally conception could only occur with sexual intercourse, but advances in medical technology allow a woman to conceive outside of utero with a sperm donor and skilled doctors.

The zygote has a total of 46 chromosomes, 23 from your partner and 23 from you. These chromosomes are responsible for your baby's traits like hair color, skin color and eye color. At this point in your pregnancy you won't be able to tell that this little seed embryo is anything but a cluster of cells, but it won't be long before the zygote grows into the beginnings of something that's recognizable as a human being.

After fertilization the zygote, or occasionally called the plant embryo, travels from the fallopian tubes to the uterus. As it moves it continues to grow and by the fourth week the fertilized egg has developed enough to be called a blastocyst. This blastocyst implants itself into the uterine wall and the placenta begins to form. It's possible to get a positive pregnancy test at this point.

The Embryonic Stage

The embryo definition is "the earliest stage of development from the time of the first cell division until birth." The origins of the word are from Greek and Latin and mean "that which grows" or "to swell, be full."

In week five the human embryo stage begins. Neural development starts, the heart begins to beat and the embryo starts to move around eight weeks. Your unborn baby will begin to develop internal organs and external body features. The embryonic stage ends at around eight or nine weeks and if you were to get an ultrasound now, you'll notice your unborn child is starting to look like a human more and more each day.

Dangers From Environmental Agents

During this development stage in pregnancy, your unborn baby is especially vulnerable to the effects of teratogens or harmful environmental agents. This is because during the embryo stage all the major organs are developing and can easily be damaged. As soon as the embryo implants into the uterus wall, it connects to your bloodstream and is exposed to what you're exposed to. Bigger doses cause more damage and the time of exposure is also a factor in the baby's development or if the baby will survive past the first trimester. Sometimes miscarriages can be caused by excessive exposure to toxins. And some embryos feel the effects of negative environmental agents more quickly and easily because of genetics.

Documenting the Embryo Stage

This part of the pregnancy is so early in the stages of pregnancy that it'll be difficult to document the growth of your baby at this point. Some new parents are especially eager to create any type of lasting record of every stage of their baby's growth. Your healthcare provider may arrange for an ultrasound around eight weeks, the end of the embryonic period. At this point you might be able to get your first image of your unborn child.

There are also some places that complete non-diagnostic ultrasounds for a fee. While not too many women get ultrasounds this early in their pregnancy, some of these locations may be able to accommodate your wishes and provide you with the earliest photo of your unborn child. The embryo will start moving around the time it transitions to a fetus, between eight or nine weeks, and you might be able to arrange for a video too.


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