Description of Twin Pregnancies

The picture below, I found Here. These are pictures of different types of twin pregnancies. 

Here are some of the terms involved:

• Monochorionic : Monochorionic twins are monozygotic twins that share the same placenta. If the placenta is shared by more than two twins, these are monochorionic multiples. These are identical twins. (Definition off wikipedia)
• Monoamniotic: identical twins that share same amniotic sac within their mother’s uterus. They also share the placenta, but have two separate umbilical cords. Monoamniotic twins develop when an embryo does not split until after formation of the amniotic sac. They are possible but extremely rare. (Definition off wikipedia)
• Dichorionic: having two distinct chorions; said of dizygotic twins. (Definition from thefreedictionary.com). These twins can still be identical, but have separate placentas. (Info from here)
• Diamniotic: having or developing within separate amniotic cavities. (Definition from thefreedictionary.com)

Based on the lab technician from my first sonogram, she said my twins were Monochorionic/Diamiotic (Mono/Di). That means, they have the same chorion but 2 separate amniotic sacs. Mine actually share a placenta.

All of the above pictures shown can be identical twins. Based on several sources I've read online (though you can never be too careful with who to trust), they have stated that dichorionic/diamniotic (Di/Di) can be either fraternal or identical. It all just depends. Confusing, right? Since mine is Mono/Di, I believe mine can only be identical twins. The doctor may read the sonogram and come up with a completely different answer, though. We shall just have to see!

Below is another picture, which I found Here.

  

In this picture, you can clearly see how the twins are formed. 

Example A...that would be a monozygotic twin. That means it comes from one egg. (I may have some of my understanding a little off on some of this, just being honest). This could be any of the 4 examples from the first picture.

Example B is an example of a dizygotic twin. Two separate eggs were dropped and fertilized. Two separate babies. Fraternal twins. 

Example C is a rare occurance. It is what's called a Polar Body Twinning (I believe). That means that an egg split and then each split half was fertilized by 2 separate sperm. That means the DNA won't be exact, but will have more of the same DNA similarities than if they were fraternal twins.

Overall, there's still a ton of stuff I have NO idea about all this. I know you're probably more confused after this post than you were before it. Sorry. I tried to explain it the best I could!