Thursday, June 19, 2008

Zygosity: why does it have to be so hard?

When we first found out our twins were, indeed, identical, I believed that the intial mistake in their zygosity was just a fluke. Their placentas were, after all, on opposite sides of the uterus. According to my OB, it was so highly unlikely that they were identical that he hadn't even considered it.
From what I understood, cases like ours were rare.
Not so.
Over and over again, I hear of twin parents who are told that their twins are fraternal, but who still simply cannot tell their twins apart. They post photos of their twins on online bulletin boards, hoping for answers.
Like us, those parents are told that the placentas were tested at the hospital. The babies can't be identical: just look at the results, the doctors say. The parents scratch their heads and try to persuade themselves that the hospital and the doctor must be right.
What doctors don't say is exactly what kind of test the hospital has conducted.
Here's what they do: Hospital simply conduct a physical test of the placentas. The lab tech studies the membranes to determine whether they were two fused placentas or one shared placenta.
That's it.
DNA has nothing to do with it.
In our case, that was a no-brainer.
Matthew and Jonathan each had clearly distinct placentas and, so, the results on my OBs computer said "fraternal." He assured us that many twins look identical when they are born and that they would differentiate as they got older.
That never happened.
If anything, they look more alike.
We finally had our boys tested when they were infants. It was easy. We received a kit in the mail for about $170 and rubbed large swabs gently inside their cheeks. We put the swabs in the test tubes the lab provided and mailed them off in the box the company gave us.
The results were supposed to take three weeks.
We learned the boys were identical a week later.
Every single one of those parents I have met online later learned through DNA testing that their instincts were correct: their twins (and sometimes two of their triplets) were indeed identical despite the protests of their OBs.
I'm not sure why some OBs still subscribe to the old theory that two placentas equals fraternal twins. Their information is outdated and so much evidence exists to prove that their methods are faulty. Just take a look at this 1999 study. The author urges OBs to change their evaluations if for no other reason, because the twins simply have a right to know.
So why does it have to be so hard?


jay_say said...

Ok... can I ask if there was a reason why you did the DNA testing? or was just to know officially? We know our boys were separate sacs but my OB said they could still be identical - depends on when the egg split if it formed separate sacs or if it was two eggs... blah, blah, blah... We just didn't want to spend the money. We tell everyone we think they're identical - I mean, just look at them...

Twinsmom said...

My strongest reason was selfish. I couldn't always tell them apart and I felt like a horrible mother. It put me at ease to know that they were identical.

Next came the medical reasons. If one develops a disease that is genetic or an allergy, we know that the other twin is at high risk as well. Also, should either one ever need an organ or a blood transfusion, we now know that the other is a perfect match.

But the final push came from my conversations with older twins. Those who were not tested said they would always wonder. One woman, in particular, was upset because she and her sister finally decided to get tested as adults, but the results came back as inconclusive. The lab told them it gets harder to determine as twins get older. They could have more sophisticated tests done, but they have no other reason to incur that expense right now. For me, it was worth the $170 for my peace of mind, their future health and their peace of mind as they grow older.

Anonymous said...

We have been told that my boys are identical - they were mono/di - one outer, two inner sacs and one placenta. I'm surprised too that this is so common - the dr told us that mono/mono and mono/di are the only cases where you can know for sure without dna tests. If we had had 2 placentas we probably would have had the testing too!
Erin posting from work :)

Anonymous said...

What company did you use?

Twinsmom said...

We used Proactive Genetics (

Lexi said...

I heard DNA testing was expensive. For $200, that would be worth it to know! Luckily our twins are b/g because now that they are looking into a genetic disorder for Laycee, they would immediately have to do so for Logan if they were identical, but since they obviously aren't we can wait it out longer.

The Myers Family said...

My dr. said ours were identical..but yet when i look at them i don't feel like they ARE identical. My dr. could tell at EIGHT weeks...he said something about a membrane between the two being very thin, which makes them identical. IF they were fraternal the membrae would be very thick. I still don't believe they are..I would LOVE to do the testing..but i just can't convince my hubby it's worth the money. I may just do it behind his back...just for myself. Perhaps a present for something.

ABC Triplets said...

Yep, you're so true about this. And going against what our OB said, we got the test, and our girls were identical. :)

Twinsmom said...

Brenda, It's worth the peace of mind. Is your birthday coming up?
J- I can't believe your OB said your girls were not identical. They look so much alike. I have two friends here in the Cincinnati area with triplets that include a set of identical twins.