My sister in law called my parents to say she’s 12 weeks pregnant and in trouble. It seems she had some bleeding over the weekend and they were concerned that she had a ectopic pregnancy.
She had an ultra sound today and they were initially quite happy that the fetus was robust with a strong heartbeat. Then they heard another heartbeat, and then another. It appears she has triplets.
From what she says, the doctors told her the triplets share a sack and are identical. They’re also concerned that the two smaller triplets won’t make it and, if they don’t, may endanger the larger fetus.
I had never heard of identical triplets. I looked on google and my initial research says they do happen but are exceedingly rare. Is that correct? Can they tell all that at 12 weeks?
I’m guessing they started as identical quads, and one of the quads spontaneously aborted early on. I really can’t think of another mechanism by which you would get multiples in an odd number. “Vanishing twin” is a pretty common phenomenon in multiple pregnancies (more common than bringing all multiples to term, in fact), so I imagine it’s not much of a stretch that there would be higher-order multiples that might “vanish”. (The embryos are said to “vanish” because they’re visible and viable during earlier ultrasounds, but appear small, misshapen, or even absent during later ultrasounds, and eventually even the gestational sac disappears).
Risk is most high for loss during the first trimester, usually due to some major chromosomal aberration, most typically a trisomy that is incompatible with life. In the case of multiples, as there are other embryos and their gestational sac(s) pumping out hormones to signal continued pregnancy, the symptoms of miscarriage can be much less severe than if a singleton is lost, or all multiples are lost simultaneously. Minor cramping and a just little bleeding or spotting are all that might indicate the loss of one or more of the embryos, and whatever is left is resorbed fairly quickly, making it difficult to know if another embryo even was there if it’s not caught on an earlier ultrasound. But, like I said, I can’t think of how one would get an odd number of identicals except via a “vanishing” embryo, so I’m guessing that’s the history.
They all would share a gestational sac that should be very evident at 12 weeks, and the individual embryos, with their yolk sacs, are also clearly visible by this time. One can easily see gestational sacs at least as far back as five weeks, and it might even be possible to see a yolk sac by then. Not long after this, the embryo is around the size of a grain of rice, and can be seen reasonably easily by ultrasound.
Crown-rump length (CRL) and pulse rate are among the best diagnostics for survival during the first trimester. Small CRL and embryonic bradycardia tend to be highly predictive of eventual loss of the embryo, especially if the numbers are well below normal, and spontaneous abortion usually happens before week 16. Again, such abnormalities frequently correlate with aneuploidies (esp. trisomies), and the damage was likely done somewhere during the first few divisions. If some of the multiples are looking small, the prognosis for their survival is indeed poorer than if they were within a normal range.
I wonder how that happens. In the earilest stages of embryonic development, epending on quite when abouts you look at them, the number of cells in a human embryo is ideally a power of 2 (day 3 has 8 cells, for instance). Splitting of the embryo much past day 12 leads to conjoined twins. If the split occurred very early in the pregnancy, the different embryos might have a noticibly different number of cells (like 6, 6, and 4, for instance). Perhaps later, during the morula-to-blastocyst stages, discrepancies of a few cells between embryos wouldn’t really matter all that much. Maybe they don’t matter early on either. It’s very interesting; I never heard of an embryo splitting into 3.
It beats me, though it is indeed very interesting. I saw an episode of Animal Planet’s The Most Extreme that stated that armadillos always have identical quadruplets, and I thought that was rather neat.
My step-father’s neice had identical triplet girls about eight years ago. I met them when they were a few months old. She could tell them apart but painted their toe nails different colors so other’s could tell them apart.
She had to carefully schedule the breast feeding so that everyone could get enough food. There were all sorts of problems like that that would never occur to you.
She belonged to a mother’s group called MOST (mothers of super twins) for families with trips or more. They were indespensible for giving out advice on how to deal with all of the issues that come up with that many babies.
I had always assumed that identical quads etc were the result of multiple splits, rather than a single four-way split. IOW a zygote splits in two, and one of those goes on to split into a further two. That means that there are never an odd number of cells and thus avoids the problems LoopyDude describes. That would also explain why, in this case, two of the foetuses are smaller than the other. The first split resulted in two embryos, one of which continued growing and one of which split into the two smaller individuals.
Trivia point: the reason armadillos have identical quads is because thay aren’t ‘real’ small animals, they are dwarf big animals. In the past armadillos were giants, and like cattle, horses and other giant animals they had only one young. As they shrank and were more prone to predation it became necessary to have litters, but you can never go home. So they worked around the problem by twinning with every single gestation.
Another half-assed solution brought to you by Ma Nature.
Identical high-order multiples are rare but absolutely possible. The Dionne quintuplets, born in rural Ontario in the 1930s, were identical, and I believe the only identical quints to this day who all survived. They were as famous as any movie stars when they were growing up.
As for how much they can see at 12 weeks - what the very best ultrasound scanners can see these days is absolutely amazing. Yes, they can see the relative sizes of the embryos, and if they can see they all share one sack they know the triplets must be identical. If they’re worried about the smaller triplets endangering the largest, that sounds to my untrained ears like a possible case of twin-to-twin transfusion syndrome, in which the blood flow to identical twin or supertwin embryos isn’t separated the way it should be. This doesn’t mean the pregnancy is doomed, but it is a serious situation and the doctors will be monitoring your sister-in-law’s pregnancy very closely.
As long as there’s more than one cell, it’s no longer the zygote, which is defined as the diploid cell resulting from the union of egg and sperm. From then until about the second month, the developing organism is properly called an embryo, though typically the very early stages get even more specific names like morula (the embryonic ball of 16-64 cells), and blastocyst (after the 64-cell stage a blastoceol develops, going from a featureless hollow sphere to the extra-embryonic trophoblast, surrionding the inner cell mass, the embryonic tissue proper, which adheres to one part of the wall of the trophoblast). I think after that it’s typically just called “the embryo”.
Interestingly, even a bit into the morula stage, the embryo is about the same size as the zygote. Instead of growing, the fission of cells in this early stage just divides the material of the zygote into an ever-increasing number of progressively small cells. Once the morula phase gets rolling the cells grow and proliferate, and the embryo increases in volume.
But that’s exactly my point. Twinning occurs when the zygote splits into two separate organisms. It must therefore occur before the embryonic stage.
Apricot, the term “embryo” is sometimes used to include the zygote as well. However, it more accurately refers to the stage after the zygote has started to divide as, Loopydude said. (See http://en.wikipedia.org/wiki/Embryo for details.)