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Saturday, January 20, 2007

Chimeras, FET twins, and Donors, oh my! (Children Mentioned)

People are so fascinated by twins that they feel the need to stop me--a perfect stranger who doesn't give off a please-talk-to-me vibe--at the mall and ask questions that always point to the same ends--do twins possess a unique bond? I'm talking about the secret-language-feeling-pain-in-your-elbow-when-your-twin-hurts-her-arm-fifteen-miles-away-completing-each-other's-sentences sort of bond. The one that makes us wonder how a person could be magically linked to another person.

Pop two babies out of your hoohaa at once and people are bound to start thinking of them as one entity. Though we don't use the term unless we are trying to avoid using their names (as you may have noticed, I never give personal info about the kids on this blog, hence why they are referred to by their situation in life), others use it liberally.

They do have a unique bond--not only their own secret language that I am attempting to break into (I can apparently use "taste my chegs!" correctly, but they turn up their nose whenever I try to use the word "bamp" in that way that Frenchmen cringe when I try to speak French), but also an ability to soothe each other that transcends anything I can do as their mother. When they were born, my son's heart often beat too quickly. His sister had bradycardia and her heart beat would dip to dangerously low levels as her brain forgot to tell her heart to beat. Put them in the same isolette? All heart problems were erased. Their heartbeats regulated themselves and most of the time beat in unison as they slept pressed together. Pull them apart and put them in different isolettes? All heart issues would return. Guess who shared a crib when they came home on heart monitors?

They move together as one unit. With the exception of a few daily toy-stealing incidents, they take care of one another. They cry when the other one is hurt or sad. They magically and silently decide when it is time to switch two toys and call out simultaneously, "switch!" When they were babies, they soothed themselves by sucking on each other's hand. Now, they soothe each other by rubbing each other's heads.

It's a bond that frankly makes me jealous. I love my husband, but we don't move together like they do. We may share our own in-jokes that create a private language, but lying together doesn't make our hearts beat in unison. He can rub my head when I'm crying, and even though I know he has my back and he's standing beside me (both figuratively and literally), I still feel alone. I feel like a single unit that is attached to other units. Based on what I've observed through behaviour and words, I think my kids feel like a single unit together that are attached to outside units like Mommy and Daddy. They're the megablock and I'm just the single Lego.

But did that coding come from being in the same womb at the same time? Or is that coding somehow part of the batch of eggs that are released? Some sort of chemical coating that gets poured on the eggs as they pop out of the follicle and make their journey down the fallopian tubes? How much about the human body do we not understand yet and how much of that comes into play when describing that special bond that twins share?

I ask this because sometimes when I ask how many children live in our house, my daughter answers "three." There are only two. And the only thing I can think of is that either she is counting one of her dolls as the third child (or she is trying to torture me since she often likes to pat my stomach and say, "nope, Mommy can't have a baby in there.") or she is remembering her triplet that I miscarried around eight weeks. Is there a part of her heart that was coded with this bond to this missing person? I know it sounds like a strange question, but just think about how little we truly understand about the brain and emotions and those connections we make between two people.

A.R.T. has created this new wave of twinship. Generally, the definition of twins states that one mother gives birth to two or more children during the same pregnancy. But what do you call...
  • (1) two children who were created via IVF where one embryo was transferred back to the biological mother, the other was transferred to a surrogate, both pregnancies miraculously took and now two children who were created at the same time are being carried in two different wombs. Yes--this is a situation I just read about. And if you say that these aren't twins, are two children who grow inside two different wombs in the same body (a la Grey's Anatomy a few weeks ago) twins?
  • (2) what about embryos that are frozen after a successful fresh cycle and transferred years later? In other words, two embryos from the same cycle--one fresh and transferred immediately, the other frozen and transferred years later. Are those two children actually twins?
  • (3) what about donor embryos? What if I have an embryo transferred into my womb and you have an embryo transferred into your womb (embryos created from eggs and sperm collected during the same cycle) and we both get pregnant and give birth. Are our kids twins?
  • (4) One FET from two different batches of embryos that were created during two different fresh cycles where one or more embryos from each batch are transferred simultaneously. Therefore, the embryos were not created at the same time, but they are conceived, carried, and delivered simultaneously. Are these children twins?

If we don't know how and when that unique bond is formed, is it possible to have sets of twins walking on this earth that don't even know that they're twins? Or have this secret longing for a person they don't even know exists? I think that's especially possible with the third scenario.

This whole question got raised the other day when we were watching Discovery Health and were confronted by this question: could you be your own twin?

Apparently, there is a little-known phenomenon that creates human chimeras. According to Wikipedia, a chimera is "an ordinary person or animal except that some of his or her parts actually came from his or her twin or from the mother. A chimera may arise either from identical twin fetuses (where it would be impossible to detect), or from dizygotic fetuses, which can be identified by chromosomal comparisons from various parts of the body. The number of cells derived from each fetus can vary from one part of the body to another, and often leads to characteristic mosaicism skin colouration in human chimeras. A chimera may be a hermaphrodite, composed of cells from a male twin and a female twin."

The Discovery Health show was examining people who are found to have two sets of DNA. This, of course, sent me straight to Dr. Google (wondering all the time, am I my own twin? Am I my own twin, damnit!?!) where I found an additional article explaining this phenomenon and how there can be different types of chimeras:

"In medicine, [a chimera is] a person composed of two genetically distinct types of cells. Human chimeras were first discovered with the advent of blood typing when it was found that some people had more than one blood type. Most of them proved to be "blood chimeras" -- non-identical twins who shared a blood supply in the uterus. Those who were not twins are thought to have blood cells from a twin that died early in gestation. Twin embryos often share a blood supply in the placenta, allowing blood stem cells to pass from one and settle in the bone marrow of the other. About 8% of non-identical twin pairs are chimeras. Many more people are microchimeras and carry smaller numbers of foreign blood cells that may have passed from mother across the placenta, or persist from a blood transfusion. In vitro fertilization (IVF) is also contributing to the number of human chimeras. To improve success rates, two or more embryos are placed in the uterus so women who have IVF have more twin pregnancies than usual. More twins mean more chimeras."

All of this is, of course, tied to A.R.T. and the increase in twins. But are there even more twins out there than we can possibly imagine? And are all these other scenarios giving birth to twins as well? In light of advances with science, do we need to start expanding the definition of twins or do these other scenarios need their own unqiue name?

Just something to think about in case you didn't have enough on your mind today...


Anonymous said...

Good questions! I've wondered about some of those, too. I saw a show a while ago which must have been about chimeras, although I don't remember that word. A woman who was trying to get federal assistance for her baby had to take a DNA test to prove she was the mother and it showed that she wasn't, even though she knew she had just given birth to the child. Ends up she was a chimera. Makes you wonder how many chimeras out there have been cleared of crimes based on DNA samples....

(And I loved reading about your kids' interactions with each other--so cute).

TeamWinks said...

Good Lord, are you trying to kill me. I didn't know I was going to have to study on a Saturday! That's a whole lot to think about. Just when you think you have an answer, you are lead to a different one. Love it!

Hmmm...very interesting point Tara has there at the end of her comment.

Ellen K. said...

The TV show "House" used the concept of an IVF chimera earlier this season. I could not resist commenting:

I can't comment on all the different ideas of what constitutes a twin. Dorland's Medical Dictionary says that "twinning" means "the simultaneous production of two (or more) offspring." That's it. What exactly does "production" mean -- fertilization? gestation? I'm inclined to go with the latter.

I love to hear about twin interactions, as my brothers are (presumably identical) twins. They sent me the same birthday card 3 years ago without realizing it, from 500 miles apart.

Anonymous said...

In response to Tara - I actually learnt about chimerism from one of those crime shows. They got the right guy in the end, though. And we all know those shows are true-to-life.

I've also had the debate with Mr Bea about the use of the word "twin" for the second child born from a single batch of frozen embryos (three or so years later). We couldn't agree. He said definitely not, I was willing to entertain the notion. (We reached a dead end when we both, simultaneously, tried to invoke the later Wittgenstein to prove our point.)

I guess it remains undecided.


Anonymous said...

Well I'm not sure. But I can tell you a real life scenario that may hurt your brain a bit more and also may explain things.

My husband's Aunt and Uncle used IVF to have their three boys. They went thru multiple fresh cycles before they were lucky with a singleton from their second fresh cycle.

But they had frozen eggs and wanted multiple children.

A few years later they took one egg from the first fresh cycle and a second egg from the second fresh cycle (where the singleton was fertilized). They both took.

So, the eldest is actually more of a genetic match to the youngest. And they look EXACTLY the same. Meanwhile the middle child, from the first fresh cycle, doesn't look like either brother.

But the twins have a very strong twin bond. And the oldest and youngest don't seem to have that same type of bond. So, using my real life scenario, I think the answer is that you need to share the living space during gestation for the bond link to occur.

Anonymous said...

How peculiar; I just had (kind of) this discussion on a message board.

I guess my take would be that twins are gestated together, whatever their genetic relationship.

the_road_less_travelled said...

Speaking of not having enough to think about. I've been having a terrible time deciding whether or not to try injects or go ahead without drugs. I think you just helped me make up my mind.

Anonymous said...

Since we now have these other wonderful new relationships, maybe we need other equally wonderful new words to describe them. Maybe "twins" isn't enough.

And I loved the story of your twins and their matching heartbeats. A reminder that the mystical is just as important as the medical.

Anonymous said...

oooh. you've made me excited about my twins.

my first thought on hearing I was having twins was even though they will not have a father (they were conceived with my eggs and donor sperm), they will have each other.
I so hope they get on like this. I wonder, though... will I be jealous of that bond? Or simply delighted that they have such a strong source of love? The latter, I hope (though also, possibly, both. life is never either/or...).

Anonymous said...

OMG, Mel. Your second question? "what about embryos that are frozen after a successful fresh cycle and transferred years later?"

Way back, just before J and I first started trying for kids, I went and saw a psychic. I asked her about children, and she told me that she didn't see babies in my immediate future, but that I *would* have children.

And then she said - "I see boy twins... but they might not come together."

I never pressed her about it - because, after all, back then I thought she was wrong - that we were going to get pregnant right away! - but lately I've been thinking... if we get pregnant with our next fresh IVF cycle... for our second child more than likely we'll need IVF again (because of our severe MF).

Maybe my psychic could be right after all. We COULD have twins. They just wouldn't come together.

I think the bond between your children is so strong because they went through so much as tiny babies. Being in the womb together, I think, is where it comes from.

Wasn't there a House episode where a person with multiple personalities was a chimera? I remember Miss E posting about something like that at one point.

Something to think about for sure.

Anonymous said...

Oh, yeah, she did. And I see she already commented too! (Should probably read the comments before putting my own up...) :)

Carla said...

Absolutely facinating! Now I have another reason to love your blog--insight, information, and very interesting and thought-provoking questions. Thanks!