Placental Confusion

This afternoon I had the follow-up ultrasound to take a better look at the triplets’ placentas. It was done at the clinic where we had the NT scan, across the street from the hospital where the MFM’s office is and where I’ll ultimately deliver. The clinic is where they have the fancy equipment.

Early this morning, I had dropped Hubs off at the airport to fly to NC for a few days. We were both a bit upset that he’d miss the appointment – the first one he hasn’t been in attendance. What if he missed some critical information about the placentas? What if they could tell the sexes today, with the hi-def machine? Well, it turns out he didn’t miss much.

No sexes. The kids were being modest, and it’s still early anyway. A couple more long weeks, then, before we’ll know. The sonographer did offer a pure guess, two boys and a girl, but it wasn’t based on the images.

And the placentas? Well, C is definitely on its own, definitely in a separate sac and with an anterior placenta. With A and B, neither the sonographer or the doctor could say for sure. If you aren’t up on your “MoMo/MoDi/DiDi” terminology, here’s a quick fetal anatomy lesson.

Boring sciencey stuff warning! And please correct me if I’ve got any of this wrong!

The placenta is the organ that provides blood and nutrients to, removes waste from, and protects the fetus. It has two parts, the maternal part that is embedded into the uterine wall and connects to the umbilical cord (which is what’s usually being referred to when one speaks of the placenta), and the fetal part that forms the protective outer membrane around the fetus called the chorion. There is an inner membrane called the amnion that also surrounds the fetus. Depending on how many days after conception a fertilized egg splits, identical twins may share one or more of these structures. Late splitters will share all of these structures (diagram A). Most commonly, identical twins will share a chorion and placenta but each have their own amnion (diagram B). Early splitters will have separate chorions and amnions, and their blood supplies to the uterus may (diagram C) or may not (diagram D) fuse together. The thing is, fraternal twins can also have a fused placenta (it occurs in over 40% of dizygotic twins, apparently), or fully separate placentas, and fraternals essentially always have separate chorions and amnions. (Not clear enough? Here’s somegood reading material.)

So, what’s our situation? Well… Here are two views of what our triplets look like all together today.

I know it’s hard to make out the babies (which are labeled… uh, yeah) – but it’s not difficult at all to see the membranes in between. The membrane width between A and B is not distinguishable from that between B and C. The doctor said she really thinks they each have their own chorion. A and B’s placentas appear to be either really close together, or they are fused. In either scenario it is not actually possible to tell whether they are identical or fraternal; only about 30% of twins with fused placentas are identical. And the doctor says for now we can’t fully rule out that they are truly sharing a placenta, so for now we err on the side of caution and monitor them as if they are, tracking their relative sizes and rechecking things in a couple of weeks. They definitely at least have their own amnion, which is good, because when they share one there’s a significant risk of entanglement in one another’s umbilical cords. If their placentas are fused but not shared, the risk of Twin to Twin Transfusion is still theoretically possible, though it doesn’t seem to actually happen.

Ideally, we find out in a couple of weeks that A and B are not the same sex and therefore definitely not identical. Since we conceived on fertility medication, all fraternal is the most likely situation. But, we just aren’t sure.

Oh yes, almost forgot to mention, I had my blood pressure checked again today and it had gone from 164/80 on Monday to 134/76 today. So the medication is doing its thing. (And I felt much better today than yesterday.)

Whew, that was long-winded for a post in which nothing was actually determined. I shall reward your patience with more pictures!

Baby A, on the bottom, was sitting on its head during the whole ultrasound. (Spine on the right of the image, leg at the top.) The sonographer was cracking up about it.

Baby B, in the middle, was again hanging out with its hands by its face.

Baby C, on top of the other two, looks like it’s in a little bubble. It also has a hand to its face, and still has more room to stretch out than the other two.


One thought on “Placental Confusion

  1. This was really interesting and helpful, Chloe. And it actually clears up one or two things my wife and I were curious about with her pregnancy.

    Also, glad to hear it about the blood pressure!

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