identical vs fraternal question

iVillage Member
Registered: 07-06-2010
identical vs fraternal question
Tue, 08-10-2010 - 9:15am
Hello I am pregnant with my 2nd set of twins! My 1st were born 14 yrs ago and resulted in beautiful healthy identical twin girls. I found out a few weeks ago I was pregnant with twins again! (scared and excited). They said these babies were fraternal and I am hoping for a boy and girl this time. I have been hearing conflicted stories that sometimes identical twins are sometimes in seperate sacs. Anyone been told they were having fraternal and ended up with identical?
iVillage Member
Registered: 07-17-2008
Tue, 08-10-2010 - 1:16pm
Congratulations again! Wow, that's neat to have twins more than once, really a blessing. :-) ID twins in separate sacs does happen, IIRC 25% of the time. I think "mygoosebumps" has ID girls that were supposedly fraternal, but don't quote me on that. If your's truly are frat, then the odds are with you that they'll be b/g. GL!


iVillage Member
Registered: 03-30-2007
Wed, 08-11-2010 - 7:58pm
It has to do with when the egg splits. If you drop two eggs and they get fertilized separately, then you have fraternal twins. If you only dropped one egg and then one sperm fertilized, you will have identical twins. Whether they end up in separate sacs or not depends on when the egg decides to split. I think it's if it splits late than you can have ID twins in separate sacs. I found out today I have 2 boys. I was told early on they were fraternal but supposedly the only sure way to know is to do a blood test after they get here, since they are the same gender. I hope that helped and didn't just confuse you more!
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iVillage Member
Registered: 04-02-2003
Fri, 08-13-2010 - 6:49pm

Hey there, congrats on your second exciting.

Here is what I learned about zygosity of twinning; it is copied/pasted from another post! I was told my girls were frat my whole pg due to them being di/di and after they were born, but because of a STRONG history (5 sets in 5 generations) of id we did the dna test and voila they ARE id.

Not sure if your twins are ID or FRAT? The only *sure* way to tell is if the twins are different genders or in the same sac. Yes, one placenta is usually an indicator of monozygotic, however u/s are not always real clear, so one placenta may actually be two fused together. If your twins are in different sacs & have different placentas a dna test after birth may be the only way to determine zygosity.

Here is a wonderful explanation:

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