As I’ve already mentioned, we decided to go with one embryo again. It’s a very daring choice, as our embryos are all B3s and there is a less than 20% chance any individual embryo of that quality will result in a baby. I suspect most couples would opt for two, as that increases the chance that you get a baby to about 40%. Of course, the rate of twins with two B3s is about 15%.
I’ve been very vocal about not wanting twins, but I would take twins over no kid at all. On that point, there’s a nice article defending twin pregnancies from IVF:
I should also note that some women who do a single embryo transfer still manage to find themselves pregnant with twins. And if that happens, you know it’s because the embryo split and you’re having identical twins. OMG.
My doctor made an interesting comment that made me think about identical twins—he suggested that use of a “hatching” blastocyst is slightly more likely to result in identical twins. Assisted hatching (using a laser to help it hatch) of day 5-6 blastys also has been associated with an increased risk of identical twins. (I’ve read that is not necessarily true with 3 day implantations.)
For “natural” (non-IVF) identical twins, the rate is about 3/1000 births. So 0.25-0.5%. Pretty rare. IVF increases the risk (or incidence, if we’re not being all anti-twin) of identical twins. Specifically, I have seen suggestions that identical twins in IVF births are about 2%.
Identical twins do not “run in families” like fraternal twins do. (I.e. there is no genetic component to egg splitting as opposed to producing extra eggs.) There is an association with older mothers—the older the mom, the more likely there is to be egg splitting and thus identical twins. The theory is that an older mom’s shell that the blasty hatches from is harder, making the inner mass break into clumps. Poor older moms! So maybe the increased identical twin risk in IVF relates to the population doing it (old moms) and maybe there really is something to the process of IVF (I’ve read articles that seem to think the latter is true).
Interestingly, the split can occur anytime in the early part of the process. An “early” split (like before day 4) usually forms identical twins that will not share a placenta. (That is good. More on that later.) Most twins split around day 4 or 5. Interestingly, twins formed during this time can be “mirror images” of each other. (So one has a mole on her right cheek, the other has the same mole in the same place on the left cheek.) Twins that split later—days 9/10—mean that they will probably share the same sac. (No good.) That only happens about 1% of the time. Even later splits (days 13-15) mean the twins might be conjoined. Very rare, also no good. [Fyi, I got all of my information from Wikipedia, so please feel free to give it as much weight as you feel is appropriate.]
Some thoughts on twins…. Okay, obviously many people (like us) who do IVF and opt for a single embryo transfer do it because we do not want twins. I know what you’re saying, “twice as nice!” Yes, but there are a lot of risks with twin births. They are harder on mom. Much harder on mom. Mom gains a lot more weight, and is at greater risk for a host of health issues such as pre-eclampsia (30% in twin pregnancy, 2-10% in singleton pregnancy), gestational diabetes (12% versus 4%), and Caesarean-section. They are also much harder on the babies. Twins are usually not full term, tend to have a lower birth weight, often spend time in the NICU, and are at risk for more health issues such as cerebral palsy (affects 4-6 times as many twins compared to singletons). And I cannot even imagine the terror of twin newborns, toddlers, teenagers, etc. The horror, the horror.
And things only get worse with identical twins. Not only are there the same risks with identical twins as there are with fraternal twins, but there are even more potential problems! Identical twins that do not share the same placenta (early splitters) are just like fraternal twins. That’s the safest kind. But once they start sharing the placenta, there’s the risk of sharing blood, and that is dangerous and can lead to death. Things only get worse if they share a sac, as their cords can get entangled, etc.
Links to articles about identical twin risks from IVF and dangers of those pregnancies:
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