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Re: Disappearing twin?From: James S Smeltzer MD (gaperina@mindspring.com)Sun Feb 17 09:20:16 2002
Wolfgang, I have seen hundreds of "vanishing twins" classified elsewhere, that were so clearly extraovular blood or fluid, without the essential properties of a gestational sac, that I would be strongly suspicious of any rate of vanishing that is over half of all twin pregnancies. The criteria I use for a gestational sac are: 1. Irregular hyperechoic outer margin (implantation site). 2. Smooth hyperechoic inner margin(blastocyst cavity or extraembryonic coelom). 3. Blood or fluid spaces with septations between. 4. Increased associated maternal blood flow at borders. OR Anything that looks sort of like a sac if it has a clearly defined embryo or less clearly defined embryo with a flicker. I have seen the last freely floating in the abdomenal blood following a tubal abortion and in the cervix with incomplete abortion. There are other grounds to believe that the spontaneous loss of twins is not excessively high: Regarding dizygotic twinning: 1. There is no reason to believe that the rate of early loss of dizygotic twins should be any higher than the rate of loss of singletons. This rate is fixed and MUST be below the rate predicted by the natural fertility rate of fertile couples of 30 to 40 percent (or MUST be less than 67%). 2. The natural rate of triplets is close to what would be predicted by the natural rate of twins. 3. Assuming an ectopic pregnancy rate of 1/100, and a twin rate of 1/100, and independence of these events, the expected heterotopic pregnancy rate should be about 1/10,000, which it is. Regarding monozygotic twinning: Early losses may be higher because we know that the rate of early loss among defective embryos is high and cloning oneself is about as far as you can go in this regard. This must result in the loss of both, as the anomaly rate in the survivor would be predicted to be high and the natural anomaly rate at birth is low. These must be regarded as rare accidents of nature because the rate of monozygotic twinning is low (about 1/300 conceptions), and independent of age, race, and living circumstances. Given our excellent ability to correctly identify the presence, location and life of an embyro before the fifth conceptional week (seventh week of LMP), I believe that the loss of monozygotic twin fetuses or pregnancies at this stage is low (under 1/100). Our In Vitro pregnancy friends tell us that the early monozygotic twin is the result of the splitting of the blastocyst by a crack in the zona pellucida, and that this is an uncommon event. Most of the phenomena that most people who have a high rate of disappearing twins call disappearing twins are the result of extraovular blood or fluid. These can be correctly identified by proper technique and the expectant families can be spared the burden of grieving for blood clots by fairly rigid adherence to the criteria I outlined above - IMHO. ;^) Jim Smeltzer
At 02:51 PM 2/16/2002 -0600, you wrote:
>Do you have sort of an actuarial lifetable of twin pregnancies starting
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