In order for a pregnancy to be successful it needs to go through a few stages. First of all, there must be a male sperm present. Then, this sperm cell needs to reach and penetrate the woman’s egg which ultimately results in it being fertilized. The newly formed zygote must then divide until it reaches its blastocyst stage. Finally, this blastocyst must implant itself in the endometrium of the uterus and continue its development into an embryo, and lastly in a healthy fetus.
At all parts of this process issues can occur which can result in abnormal development or even abortion.
Now, let’s summarize all the stages and then dive deeper into each one of them and see their peculiarities and potential issues:
- Blastocyst Development
- Blastocyst Implantation
- Embryo Development
- Fetal Development
Fertilization is when the male and female cells bind together. The product is called a zygote, no matter if the process happens naturally in a female’s body or in vitro. During ovulation, women release an egg in one of their fallopian tubes. After that, if ejaculation occurs, sperm cells find their way to the egg cell and penetrate it, leading to fertilization.
If you want to know more about this process and its various stages, head out to our article on the topic.
After everything is done, the zygote starts moving towards the uterus. At the same time cells starts dividing entering the next stage – a blastocyst.
There are a lot of issues that can occur during this process that will prevent fertilization but they all have the same final result – failure to initiate full blown pregnancy. Fertilization will not occur if there is no egg after the female’s ovulation or the sperm has low count or isn’t potent enough. Poor sperm motility or if the cervical mucus isn’t thin enough will also result in fertilization failure.
After a successful fertilization the embryo will be created by a few cells that will keep on dividing forming a structure called a blastocyst. The blastocyst has inner and outer cell layers (as well as fluids). It stays inside the zona pellucida during the maturation. Think of it as an egg shell which protects the egg until its mature enough to move on to its next stage. The outer layer of cells will create the placenta and the surrounding sack tissues which will support the fetal development.
The inner layer of cells will become the various organs of the baby and form all its tissues such as its muscles, bones, etc. These inner cells grow way faster than the outer layer ones and go through many morphological changes in their path to conversion. The more they specialize the tighter the blastocyst structure becomes. At this point the zona pellucida breaks apart and the blastocyst moves to the uterus where it implants itself in the wall.
The dividing cells can just stop dividing and put everything down to a halt. This is called “blastocyst arrest”. This process is directly linked to genetic abnormalities in either the female egg or the sperm cell.
When it reaches its final goal, the blastocyst implants itself in the uterus’ wall. As we pointed out, the external cell layer of the blastocyst along with the uterine inner lining combined create the future placenta that will feed the fetus.
Sometimes a fertilized egg implants into the uterine wall but fails to continue its division progress. This is called a blighted ovum. It happens due to chromosomal abnormalities in any of the parent cells. If the endometrium is damaged the fertilized egg won’t be able to properly implant itself and will be lost. Sometimes the endometrium can even deny the entry of the egg, which is thought to be a mechanism to select the healthy eggs.
To learn more about cryopreservation and storing of embryonic cells, head out to our Main Page.
After the blastocysts finishes its process of implantation into the uterus it turns into a structure called an embryo. This is the period in which internal organs and other structures begin to form.
First, the mouth, jaw and throat are created. Then the heart and vessels start to form followed by the arms, fingers, legs, toes, and even the eyes.
Some of the final things that begin their development are the spinal cord and digestive tract along with the rest of the sensory organs.
On the 10th week cartilages begin turning into bones. After 2 more weeks the embryo goes to its final stage of development and is now called a fetus.
Problems here can happen as early as the first few weeks. With the creation of so many organs and systems and specialized cells, there is lots of room for errors. This tiny organism is extremely vulnerable to external factors at this point (such as radiation, poisoning, etc.). The genetic abnormalities here have a wide range of possibilities from mutations to lack of important structures such as a brain or a heart.
Now, it’s time to move on to the final stage:
The Fetal Development
By this week (12th) the fetus has all its structures and organs created. Those organs will still need to grow, but it is important that they are there already. At this point the hands and legs are entirely developed and can be visualized with an echography.
12 more weeks and your little baby will respond to sounds and will measure roughly 12-14 inches and weight around 5 pounds. It will start changing its position and by the eight month it is called a baby. The brain finishes its development and now the baby can see and hear, but the lungs will need some more time.
Again, at this stage, the fetus/baby is extremely vulnerable to external factors such as shock, hits, radiation, food poisoning, malnutrition, etc.