Do twins have to be sharing an amniotic sac to be identical?

Quick just answer one

I’ll go ahead and just tell you. I learned this when my sister had twins.

Okay. So the answer is NO. They don’t.

Identical twins come from one egg, one sperm. But there are different types of identical twins. And although identical, the type of identical twin that they are can determine JUST how identical they are.

Science believes the type of identical twins you get just depends on how long it took for the egg to split into two embryos.

Conjoined twins are thought to be what happens when that egg just splits wayyy too late after conception.

Fun fact that I’m surprised ALOT of people do not know

Identical twins CANNOT be opposite sexes

One egg and one sperm means either boy or girl. It cannot mean both sexes. One sperm fertilized that egg and it only carried X or Y chromosomes. Period.

If fraternal twins come out looking very much alike, it’s just like I look a lot like my sister but we are 6 years apart and share only so much DNA, when identical twins share 100% of their DNA.

If the twins have separate inner sacs. They had more of a chance to move around in the womb early on before they implanted.

The uterus, its packed thick with DNA. Every man who’s ever ejaculated inside of you left his DNA in there. (Sorry)

If you’d ever been pregnant before, there’s even more DNA for these twins to roll around in.

In those early days, their DNA has chances to mutate and change which is why some twins have slight differences in appearance.

This is why you can have a set of identical twins and have one with a genetic abnormality. It shouldn’t make any sense, but like I said the uterus is full of DNA and for some reason if you don’t implant into moms uterus ASAP you are at more risk for being genetically different when you are born vs the second you are conceived.

Zygotes are so capable of changing and mutating before they implant. But those identical twins that took their time and split after mom created a comfy spot for them? (Implantation) Those twins will share one placenta and one amniotic sac. And they will be absolutely genetically identical, and are sometimes referred to as mirror twins.

These twins, as well as twins who share one placenta but have separate sacs.. they are high risk twins because they share one food supply. These pregnancies need to be monitored by a specialist to make sure one baby isn’t taking nutrients from the other. It’s called twin to twin transfusion.

There is a surgery that can correct twin to twin transfusion, but I hope it’s not often necessary.