TRAP

(in which I talk about strange and disturbing fetal anomalies, so don't read if that kind of thing gives you nightmares.)

There is a disease entity called Twin Reverse Arterial Perfusion, or TRAP. It is, thankfully, rare: 1/35000 pregnancies. The other name (likely, the older, less scientific name) for it is acardiac twin. Basically, the pregnancy consists of a normal twin with heart, and a very abnormal twin that... doesn't have one.  The abnormal twin - the acardiac twin - only continues to live (if that's the appropriate term) because the twins have a placenta that connects, and in fact, shares a blood system. So the normal twin - the "pump" twin - has a heart that moves the blood around for both of them.

When I say "very abnormal", it's hard to know how to explain. There can be structures in the acardiac twin that are recognizable - a skull, or a leg - but there might not be, and even if there were, they become unrecognizable because they get swollen and deformed as the pregnancy progresses. The acardiac twin doesn't have a brain, so far as we would recognize one. It is a pregnancy that would have been long lost - would never have developed - but for the fact that it is attached to something else that keeps it going.

The tragedy here is not the acardiac twin, although that is sad. The tragedy is the pump twin, which over time, has a heart that is working too hard to fill two systems, and over time, gets sick, and fails. That fetus then dies.

So what do you do? If you need to, you can do some intra-uterine surgery - use a laser to block the acardiac twins cord, or use radiofrequency ablation to burn it, or somehow, break the connection between the two parts of the pregnancy. There are risks, and it doesn't always work, but it can be a way to get a healthy baby out of this very complicated pregnancy.

I'm not feeling poetic, but if I was, there would be plenty here to work with: heartlessness, deformity, salvage.
I'm not feeling political/theological, but if I was, there would be plenty here to work with about the murkiness of in-utero life.

I'm feeling sad, and mostly wishing we didn't call this a twin pregnancy. I wish we called the acardiac twin a placental growth or something like that.You could argue that that would be inaccurate, and you'd be right. But isn't the word twin, in its own way, completely inaccurate and unfair, and making this much, much harder than it needs to be? All I know is that these words in the counselling of a relatively unsophisticated patient made our plan sound needlessly ruthless. And that changing them would be an act of charity, and arguably, of honesty.