Friday, January 05, 2007

Who knew?

Back in September a woman gave birth to triplets from her TWO wombs. Lest you think I'm as bad as "Discovery Health," I mention it for two reasons. One, because I had not heard of the condition (which is less rare than you'd think: 1 in 1,000 women has two uteruses, according to the article). Two because the fact that she conceived in both wombs simultaneously is especially unique.

The article explains that the dual uterus condition results not from duplication of the organ but from improper fusion of it during development. Just as failure of the roof of the mouth to close during gestation produces the cleft palate condition, incomplete union of the two growing sides of the uterus produces two. I did not know that.

But if I understand the description of how the condition arises, it makes sense that each "half" uterus would be connected to one ovary. There wouldn't be four ovaries, because they are farther from the body's midline, where things join. There would be two ovaries, the left one connected to the left uterus, the right one connected to the right. In normal ovulation the ovaries take turns ovulating -- the left one month, the right, the next. It would follow, then, that with a bifurcated uterus, only one "side" at a time would have an egg released to it. To impregnant both uteruses, both ovaries would have to release eggs in the same cycle.

This is certainly not unheard of. In fact, I think it is partly responsible for the increase in multiple births as women age: the ovaries stop taking turns. But the woman in this story is 23. Irrelevant to the result I suppose. Whatever the reason, she had eggs in both uteruses (or fallopian tubes) when the sperm arrived. That one of the fertilized eggs further separated into indentical twins makes the case even more unique. Indeed, it's the only one on record of multiples from two uteruses.

Just now I had a further thought: could the same genetic modification that led to the mother's atypical uterine development also have been responsible for the one embryo's divition into twins? Fraternal twins run in families. The tendancy to release multiple eggs is heritable. Identical twins do not. This indicates that the division that produces twins is not passed on in the genes...which blows my theory.

But, hey, what would one be if one didn't hypothesize?

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5 Comments:

Blogger Tara said...

I was also fascinated by that story and several I had heard previously. A while back I did some research to learn more. There is quite a spectrum of these so-called "Mullerian defects." I found this in an older study: "The incidence of uterine congenital anomalies because of mullerian defects in the normal fertile population is 3.2% (22/679). Twenty (90%) of them are septate uteri, whereas a bicornuate (5%) and a didelphys uterus (5%) have been also found in this population." There are lots of links to be found if you google it.

It is amazing to me how complex our fetal development is!

2:50 PM  
Anonymous Anonymous said...

The only time I have ever heard of this was on an episode of Grey's Anatomy earlier last fall. To complicate the issue further (and to add make it more dramatic)they had the babies at different gestational ages (about a month apart, I think) and with different baby daddys!

Its sad my only reference is television.....

7:12 PM  
Anonymous Julie said...

Ha ha, t$, that was my first thought, too: what if the babies had different fathers. ;-)

8:20 AM  
Blogger Bekah said...

There has been more recent speculation that there may be a hereditary component to identical twinning, but it's just not discernible yet. See: http://www.twinsnetwork.com/index.php?option=com_content&task=view&id=21&Itemid=25

2:48 PM  
Blogger Diane said...

Interesting

11:12 AM  

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