The first delineation of twin to twin transfusion syndrome was by a German obstetrician, Friedrich Schatz. In 1875 he described the placental "third circulation" and more fully explored this concept in 1886. Schatz injected the fetal placental blood vessels of twins and showed clearly that there are inter-twin blood vessel anastomoses, most commonly artery-to-artery communications. And these occurred only in "identical" twins, and only in those (2/3) who possessed a so-called monochorionic twin placenta. But, when he further studied the vascular anastomoses, he saw that there occurred also artery-to-vein communications. Because these traveled from one twin to the other, the possibility of "transfusion" from one twin to the other was assured. These transfusions took place through a "villous district" of the placenta and, because they could not be seen directly from a surface inspection of the blood vessels in the placenta, he called this the "third circulation. Then, he made a remarkable discovery. He saw a set of twins with the classical twin to twin transfusion syndrome and described this in a very long meticulous paper. These twins were grossly discordant, one twin being edematous, the other shriveled up. The edematous twin passed away in 12 hours and urinated all the time and had a hugely distended bladder at autopsy. The other, growth restricted baby passed away in 53 hours, never urinated and had an empty bladder. Schatz inferred that the polyhydramnious (distension of the amnionic cavity with fluid and reason for premature delivery) was due to excessive intrauterine urination of the "recipient" of the transfusion from the "donor" twin who was atrophied and was then already described as the "stuck twin", because there was no fluid in which he could move before birth. This concept was quickly confirmed by Hyrtl, an anatomist from Vienna who produced an atlas of injected twin placentas in 1870. The twin to twin transfusion syndrome was delineated as the most important determinant of growth disparity between identical twins.

Since those days, many scientific articles have appeared that clearly show the veracity of these deductions. There is, for instance, a series of articles by Naeye, a pathologist from Pennsylvania who analyzed the bodily structures of twins passing away from twin to twin transfusion syndrome. He showed clearly that the chronic deprivation of blood and nutrients from the donor to the recipient twin in their placenta was the cause of small organs in one and much enlarged organs in the recipient twin. Blood flow studies have since been done by Doppler ultrasonography to show the flow from one twin to the other. Blood pressure differences and, of course, blood content differences (hematocrit) have been identified.

Twin to twin transfusion syndrome is not only problematic because the twins are born prematurely because of the massive hydramnios that develops, but also, because there is a chance that one twin passes away in utero, the donor, with the other surviving. When that happens, the hydramnios disappears quickly, but there is great likelihood that the survivor will bleed (backwards through the anastomoses) into the donor, partially exsanguinate rapidly and suffer brain damage with subsequent cerebral palsy.

All these studies led to attempts at "curing" the twin to twin transfusion syndrome before birth by elimination of the anastomoses. The most innovative and completely curative approach has been that developed by De Lia (1983). He experimented with sheep, then monkeys and eventually confronted the human syndrome by the obliteration of the blood vessel communications on the placental surface. This required their identification through fetoscopy and then using a laser beam to coagulate the blood within the "third circulation". When this is done successfully, the "donor" twin begins to urinate immediately, the hydramnios disappears (avoiding premature delivery) and the twins grow more normally. Moreover, the possibility of exsanguination by backwards bleeding is forestalled.

There have now been hundreds of pregnancies with twin to twin transfusion syndrome so treated, with a much better survival rate than when no treatment is done or when other treatment such as amniocentesis, digitalis, etc., are used. There is no doubt that this therapy will be improved as more surgeons gain experience and when ultrasonography improves to the point that one can actually demonstrate the "third circulation" more precisely.

Prior to Schatz and Hyrtl, there was another German physician, Hueter (1845) who described the placenta, but it was not universally accepted as delineating the topic. In fact, there had been many individual cases described in earlier centuries, but Schatz and Hyrtl were probably the most important individuals. For instance, Spaeth (1860) also published many (185) twin placentas and used wax injection. Thus, anastomoses were well accepted when Schatz and Hyrtl worked; but their specific involvement in disease was not recognized. Schatz was an obstetrician and had been somewhat controversial because he was so outspoken. But, he published a lot and was very observant. He was so good that after his death an "annotated bibliography" of his work occupied one whole copy of the Archiv fuer Gynaekologie.

Schatz was adamant that one MUST inject and then immediately record the finding. He was adamant that one must warm the placenta and wash out the blood as quickly as possible after the delivery. He used "colored solutions", the kind he used I do not know. I like milk because it is easily seen, easily washed out, can be visualized microscopically and it is always available. BUT, one cannot easily inject the ENTIRE placenta. It takes too much fluid, the placenta is often disrupted and isolation of a few "probably" regions is best.

The "third circulation" was used by Schatz as to mean that there was a portion of blood circulation through both babies (of monochorionic twins) and he thought that this was of about 5-10%. But, those were very early insights into a problem that was just being clearly delineated.

A "shared" cotyledon of such twins is one small region in the placenta that is fed by the artery of one twin (the donor) and drained by the vein into the other twin (the recipient). It can be a multiple situation, and they may go into opposite directions; thus the degree and time of onset of the clinical twin to twin transfusion syndrome varies greatly. Schatz already saw that vein-to-vein anastomoses are the LEAST common, by a long shot, and all of us find the same.

Schatz did not have ultrasound, but having good clinical skills and examining carefully all the placentas made him interpret the importance of the anastomoses. And, it must be said that we still are not able to identify the anastomoses by ultrasound. It must also be said that in the last century, people became much more interested in the physiology of the placenta and gradually, cumulatively accumulated findings that allowed Schatz and Hyrtl to make their deductions. It was a very slow process though.

Schatz was an obstetrician and THEY were generally the only ones who studies placentas, as they were available to them; the anatomists were quite secondary, and embryology was rudimentary and occupied itself with other topics.

Yes, we still inject placentas, with milk or barium, few use latex as this is so time-consuming and difficult. And, if one REALLY wants to understand the mechanics of placental circulation, then one MUST inject placentas. Otherwise, one will never get the understanding for the reasons of the existence of twin to twin transfusion syndrome or how to treat it with laser.

Price in 1950 was interested in the reasons why twins pass away so much more often, why they are often discordant and why anomalies occur. He was more of a statistician and pointed out the PRE-natal causes of twin problems, rather than the mechanics of birthing (then popular topics, e.g. how long should one wait between twin 1 delivery and twin 2, etc.). Price laid the blame on PRE-natal problems, but he did not follow the twin to twin transfusion syndrome.

Schatz was also interested in and explained the acardiac twins. Acardiacs (no heart) occur ONLY in monochorionic twins and are obviously nonviable. He showed that they possessed one artery-to-artery and one vein-to-vein communication in the placenta and that, early in embryonic life, the pressure in the artery of the larger twin reversed the circulation of the other twin and made him lose his cardiac development. That was one of the major reasons for Schatz' engagement in twins.

Twin to twin transfusion syndrome is not being "tracked now" other than by those who do the laser therapy. It is regrettable and should be a project that someone should take on, especially the development of cerebral palsy. (The Foundation is now doing this). The easiest way to anticipate twin to twin transfusion syndrome is the rapid development of hydramnios in mid-pregnancy and then the diagnosis of diamnionic-monochorionic placentation. It can then be verified by different-sized hearts at birth.

Naeye is a pathologist (recently retired at Hershey). He weighed and measured the sizes of all organs and compared them with one another (in the twins) and with normal-sized infants; he then measured the size of the heart fibers, cell size in kidneys, adrenals, etc. It showed striking differences from normal and between the twins. From this, he had a good correlation with the plethora of the recipient twin, and with the hypertension these twins have in utero. With all the blood transferred to the recipient, he becomes blood-overloaded (has more hemoglobin, higher hematocritis) and he tries to get rid of that fluid by urinating more,; thus the blood becomes thicker, thus thrombosis can occur. He develops a bigger heart in order to push the increased blood around, just as every hypertensive body does. Some blood pressures have been recorded, but that is difficult in newborns and thus not often done. This occurs in utero and only after birth are the pressures gradually equalizing. Thus, one often removed blood from the recipient and infused it into the anemic donor.

Anastomoses are of course blood vessel communications between the two fetal circulations on the surface of the placenta. There are arteries and veins. The arteries come from the baby's heart and the veins bring blood back from the placenta to the baby; the baby pushes this blood around with his heart. An artery-to-artery anastomosis is one in which the artery of one twin meets and connects with one from the other twin on the surface of the placenta. The same applies to a vein-to-vein anastomosis. A "common villous district" ("shared cotyledon:") is one in which a district of the placenta is being injected by blood from one twin(the donor), goes through the villous tissue of the placenta and then is drained from that district into the recipient twin. THAT is what is the basis for the twin to twin transfusion syndrome. Atrophied means "shriveled up: so to speak, smaller, shrunken.

References

De Lia, J.E., Kuhlmann, R.S., Cruikshank, D.P., O'Bee, L.R.: Placental surgery: a new frontier. Placenta 14:477-485, 1993

Hyrtl, J.: Die Blutget,, e der Menschlichen Nachgeburt in normalen und abnomen Verh,, Itnissen, Braumller, Vienna, 1870

Naeye, R.: Organ abnormalities in a human parabiotic syndrome. Amer. J. Pathol. 46:829-842, 1965.

Price, B.: Primary biases in twin studies: review of prenatal and natal differences-producing factors in monozygotic pairs. Amer. J. Hum. Genet. 2:293-352, 1950.

Schatz, F.: Die Gef,,ssverbindungen der Placentarkreisl,,ufe eineiiger Zwillinge, ihre Entwicklung und ihre Folgen. Arch. Gyn,, kol. 27: 1-72, 1886.

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Written by Kurt Benirschke, MD - UCSD University Medical Center
© 1999, 2000, 2001, 2002, 2003, 2004 The Twin to Twin Transfusion Syndrome Foundation