双胎間輸血症候群, twin to twin transfusion syndrome, twin-to-twin transfusion syndrome
出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2015/12/02 10:56:10」(JST)
双胎間輸血症候群(そうたいかんゆけつしょうこうぐん、英語: Twin-to-twin transfusion syndrome; TTTS)とは、一卵性双胎児が胎盤を共有した状態(一絨毛膜双胎)のときに、共通胎盤上の吻合血管を通して引き起こされる血流移動のアンバランスによって両児の循環不全を生じる病態を指す。
胎盤を共有するというのは以下のような状態を指す。胎児は臍帯動静脈を介して胎盤の小部分である胎盤小葉でガス交換や物質交換をしているが、一絨毛膜胎盤の胎盤小葉では一方の児から流れ込んできた血液が、他方の児の側に戻っていくことがしばしばある。すなわち両児間で血液が行き来し、循環を共有しているということになる。このような場合、全例ではないが、それぞれの胎児への血液供給のバランスは往々にして取りにくくなり一方の胎児からもう一方の胎児へ胎盤を通して血液が流れることがある。すると受血児(血液が流れ込む先の胎児)は多血症からうっ血性心不全、浮腫、羊水過多等を生じ、供血児(血液の流れの元となる方の胎児)は循環血液量の減少によって羊水過少になり、悪化すると発育不全を起こして小さくなる。このように両児の間で血液の流れが生じるので、「一方からもう一方へ輸血しているようなものである」という考え方が病名の由来である。
なお、血液循環バランスの乱れる経過が緩やかである場合を慢性TTTSに、何らかの原因により急激に供血児から受血児に血液が流れ込む病態を急性TTTSに分類されていたが、この概念は一般的ではない。
超音波検査で一児の羊水過多ともう一児の羊水過少を同時に認めた場合に診断される。また重症度分類としてQuintero分類が用いられる。両児の体重差や生後のヘモグロビン値は診断に用いられない。受血児は心不全、胎児水腫を呈することがあり、また供血児は腎不全、発育不全などの症状が代表的であるが、症例によって異なる。
受血児の羊水過多による流産、早産のリスクが高い。一般に保存的治療では胎児の予後は不良である。
双胎間輸血症候群の標準的な治療法は連続的羊水除去術であるが,近年,新しい胎児鏡下レーザー手術が提案され、欧米と日本において徐々に普及しつつある。
連続的羊水除去術は、羊水過多を起こしている受血児側の羊水腔に針を刺し、羊水を1-2L吸引除去するものである。羊水過多の改善により陣痛発来や前期破水を予防し、胎児が胎外生活可能な時期(妊娠24-26週以降)まで妊娠の延長を目指すものである。受血児側の羊水過多の軽減が一時的に得られても、数日で再貯留することが多く、通常1週間に1-2回、繰り返し羊水吸引除去を行う必要がある。
胎児鏡下レーザー手術は,正式には胎児鏡下胎盤吻合血管レーザー凝固術(Fetoscopic laser photocagulation of placental communicating vessels: FLP)といい、麻酔下に母体腹壁をとおして子宮内にスコープを挿入して、胎盤上にある両児間の複数の吻合血管をレーザーを用いて凝固焼灼していく手術である。手技に高度な熟練を要すること、母体と胎児にリスクが存在することなどいくつかの問題点が存在するが、手術に成功すれば病態自体を改善することになる。欧米と日本での報告をまとめると、少なくとも一児が生存する割合は80%対60%とレーザー手術がやや上回る程度[要追加記述]であるが、助かった児がその後神経学的後遺症を残す割合が5%対25%というようにレーザー手術の方が有意にすぐれている[要追加記述]といえる。
日本での胎児鏡下レーザー手術は2002年に聖隷浜松病院(静岡県浜松市)にて本格的に開始され、現在、Japan Fetoscopy Group(JFG)に集う病院にて行われている。JFGに所属する病院は,先の聖隷浜松病院のほかには,北から、宮城県立こども病院(宮城県仙台市)、国立成育医療センター(東京都世田谷区)、国立病院機構長良医療センター(岐阜県岐阜市)、大阪府立母子保健総合医療センター(大阪府和泉市)、川崎医科大学川崎病院(岡山県岡山市)がある。合わせてすでに500例以上の施行実績がある。2008年からは北海道大学病院(札幌)でも開始された。
この項目は、医学に関連した書きかけの項目です。この項目を加筆・訂正などしてくださる協力者を求めています(プロジェクト:医学/Portal:医学と医療)。 |
Twin-to-twin transfusion syndrome | |
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Illustration of a Fetoscopy and laser ablation of connecting vessels in Twin-to-twin transfusion syndrome
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Classification and external resources | |
Specialty | pediatrics |
ICD-10 | O43.0, P02.3, P50.3 |
ICD-9-CM | 762.3 , 772.0 |
DiseasesDB | 32064 |
MedlinePlus | 001595 |
eMedicine | med/3410 |
MeSH | D005330 |
Twin-to-twin transfusion syndrome (TTTS, also known as Feto-Fetal Transfusion Syndrome (FFTS) and Twin Oligohydramnios-Polyhydramnios Sequence (TOPS)) is a complication of disproportionate blood supply, resulting in high morbidity and mortality. It can affect monochorionic multiples, that is, multiple pregnancies where two or more fetuses share a chorion and hence a single placenta. Severe TTTS has a 60–100% mortality rate.[1]
Based on recent (2005) US NCHS data,the rate of multiple births is now approximately 3.4% (4,138,349 total births, of which 139,816 were twins or higher-order multiple births). The majority of identical twins share a common (monochorionic) placenta, and of these approximately 15% go on to develop TTTS. By extrapolating the number of expected identical twins (about one-third) from annual multiple births, and the number of twins with monochorionic placentae (about two-thirds), and from these the number thought to develop TTTS (about 15%), there are at least 4,500 TTTS cases per year in the U.S. alone: 139,816 X .33 X .66 X .15 = 4,568 cases of TTTS per year in U.S. (involving more than 9,000 babies.) Since spontaneous pregnancy losses and terminations that occur prior to 20 weeks go uncounted by the C.D.C., this estimate of TTTS cases may be very conservative. Although infertility treatments have increased the rate of multiple birth, they have not appreciably diluted the expected incidence of identical twins. Studies show a higher rate of identical twins (up to 20 times with IVF) using these treatments versus spontaneous pregnancy rates.
One Australian study, however, noted an occurrence of only 1 in 4,170 pregnancies or 1 in 58 twin gestations. This distinction could be partly explained by the "hidden mortality" associated with MC multifetal pregnancies—instances lost due to premature rupture of membrane (PROM) or intrauterine fetal demise before a thorough diagnosis of TTTS can be made.[2]
As a result of sharing a single placenta, the blood supplies of monochorionic twin fetuses can become connected, so that they share blood circulation: although each fetus uses its own portion of the placenta, the connecting blood vessels within the placenta allow blood to pass from one twin to the other. It is thought that most monochorionic placentae have these "shared connections" that cross the placenta, with the net flow volumes being equal between them. This state is sometimes referred to as "flow balance". Depending on the number, type and direction of the interconnecting blood vessels (anastomoses), blood can be transferred disproportionately from one twin (the "donor") to the other (the "recipient"), due to a state of "flow imbalance" imparted by new blood vessel growth across the placental "equator", the line that divides each baby's proportion of the shared placenta. This state of transfusion causes the donor twin to have decreased blood volume, retarding the donor's development and growth, and also decreased urinary output, leading to a lower than normal level of amniotic fluid (becoming oligohydramnios). The blood volume of the recipient twin is increased, which can strain the fetus's heart and eventually lead to heart failure, and also higher than normal urinary output, which can lead to excess amniotic fluid (becoming polyhydramnios).
TTTS usually develops during the period of peak placental growth, starting in week 16 & proceeding through week 25, after this the placenta's growth decelerates, essentially stopping just after week 30. While TTTS has occasionally been detected beyond this timepoint, it is thought that its occurrence beyond week 30 may be due to a placental embolism that upsets the flow balance of the shared connections between the babies. TTTS is potentially lethal to either or both twins, no matter when it is detected. However, when detected past week 25, emergency delivery may be considered to rescue the babies if the TTTS is severe.
Other than requiring a monochorionic twin (or higher multiple) pregnancy, the underlying causes of TTTS are not known. It is not known to be hereditary or genetic.
Some doctors recommend complete bed-rest for the mother coupled with massive intakes of protein as a therapy to try to counteract the syndrome. Research completed shows these nutritional supplements do work. Diet supplementation was associated with lower overall incidence of TTTS (20/52 versus 8/51, P = 0.02) and with lower prevalence of TTTS at delivery (18/52 versus 6/51, P = 0.012) when compared with no supplementation. Nutritional intervention also significantly prolonged the time between the diagnosis of TTTS and delivery (9.4 +/- 3.7 weeks versus 4.6 +/- 6.5 weeks; P = 0.014). The earlier nutritional regimen was introduced, the lesser chance of detecting TTTS ( P = 0.001). Although not statistically significant, dietary intervention was also associated with lower Quintero stage, fewer invasive treatments, and lower twin birth weight discordance. Diet supplementation appears to counter maternal metabolic abnormalities in monochorionic twin pregnancies and improve perinatal outcomes in TTTS when combined with the standard therapeutic options. Nutritional therapy appears to be most effective in mitigating cases that are caught in Quintero Stage I, little effect has been observed in those that are beyond Stage I.[3]
A staging system proposed by fetal surgeon Dr. Ruben Quintero is commonly used to classify the severity of TTTS.[4]
Stage I: A small amount of amniotic fluid (oligohydramnios) is found around the donor twin and a large amount of amniotic fluid (polyhydramnios) is found around the recipient twin.
Stage II: In addition to the description above, the ultrasound is not able to identify the bladder in the donor twin.
Stage III: In addition to the characteristics of Stages I and II, there is abnormal blood flow in the umbilical cords of the twins.
Stage IV: In addition to all of the above findings, the recipient twin has swelling under the skin and appears to be experiencing heart failure (fetal hydrops).
Stage V: In addition to all of the above findings, one of the twins has died. This can happen to either twin. The risk to either the donor or the recipient is roughly equal & is quite high in Stage II or higher TTTS.
The Quintero staging does not provide information about prognosis, and other staging systems have been proposed.[5]
Various treatments for TTTS include:
Expectant Management
This is equivalent of zero intervention. It has been associated with almost 100% mortality rate of one or all fetuses. Exceptions to this include patients that are still in Stage 1 TTTS and are past 22 weeks gestation.
Serial Amniocentesis
This procedure involves removal of amniotic fluid periodically throughout the pregnancy under the assumption that the extra fluid in the recipient twin can cause preterm labor, perinatal mortality, or tissue damage. In the case that the fluid does not reaccumulate, the reduction of amniotic fluid stabilizes the pregnancy. Otherwise the treatment is repeated as necessary. There is no standard procedure for how much fluid is removed each time. There is a danger that if too much fluid is removed, the recipient twin could die. This procedure is associated with a 66% survival rate of at least one fetus, with a 15% chance of cerebral palsy and average delivery occurring at 29 weeks gestation.
Septostomy, or Iatrogenic Disruption of the Dividing Membrane
This procedure involves the tearing of the dividing membrane between fetuses such that the amniotic fluid of both twins mixes under the assumption that pressure is different in either amniotic sac and that its equilibration will ameliorate progression of the disease. It has not been proven that pressures are different in either amniotic sac. Use of this procedure can preclude use of other procedures as well as make difficult the monitoring of disease progression. In addition, tearing the dividing membrane has contributed to cord entanglement and demise of fetuses through physical complications.
Laser Therapy
This procedure involves endoscopic surgery using laser to interrupt the vessels that allow exchange of blood between fetuses under the assumption that the unequal sharing of blood through these vascular communications leads to unequal levels of amniotic fluid. Each fetus remains connected to its primary source of blood and nutrition, the placenta, through the umbilical cord. This procedure is conducted once, with the exception of all vessels not having been found. The use of endoscopic instruments allows for short recovery time. This procedure has been associated with 85% survival rate of at least one fetus, with a 5% risk of cerebral palsy and average delivery occurring at 33–39 weeks' gestation.
Twin anemia-polycythemia sequence (TAPS) may occur after laser surgery for TTTS (post-laser form). The spontaneous form of TAPS complicates approximately 3 to 5% of monochorionic twin pregnancies, whereas the post-laser form occurs in 2 to 13% of TTTS cases.[6][7] The pathogenesis of TAPS is based on the presence of few, minuscule arterio-venous (AV) placental anastomoses (diameter <1mm)[8] allowing a slow transfusion of blood from the donor to the recipient and leading gradually to highly discordant Hb levels.[9]
Umbilical Cord Occlusion
This procedure involves the ligation or otherwise occlusion of the umbilical cord to interrupt the exchange of blood between the fetuses. The procedure is typically offered in cases where one of the fetuses is presumed moribund and endangering the life or health of the other twin through resultant hypotension. Use of this treatment has decreased as TTTS is identified and treated in earlier stages and with better outcomes. When used, it is associated with an 85% survival rate of the remaining fetus(es) with 5% risk of cerebral palsy and a 33–39 weeks of gestation at delivery.
A recent review found that laser coagulation resulted in fewer fetal and perinatal deaths than amnioreduction and septostomy, and recommended its use for all states of TTTS.[10]
TTTS was first described by a German obstetrician, Friedrich Schatz, in 1875. Once defined by neonatal parameters—differences in birth weight and cord hemoglobin at the time of delivery—TTTS is now defined differently. Today, it is known that discordant fetal weights will most likely be a late manifestation, and fetal hemoglobin through cordocentesis is often equivalent in the twin pair even in severe TTTS.[2]
A painting known as the De Wikkellkinderen (The Swaddled Children), from 1617, is thought to represent a depiction of TTTS.[11] The drawing shows twins that appear to be identical, but one is pale (possibly anemic), while the other is red (possibly polycythemic). Analysis of the family histories of the owners of the painting suggests that the twins did not survive to adulthood, although whether that is due to TTTS is uncertain.
Although somewhat of a stretch, due to the detail of "magical birthgiving" in the folklore, an example of TTTS might have been noted ages before Schatz classified it or the painting "De Wikkellkinderen" illustrated, as an old Norse fairy tale, "Tatterhood", seemed to explain it, with one of the two girls being lovely but weak (pale skin and delicacy of anemia has often associated with how girls were most expected to be at the time) and the other one, the title heroine, was considered hideous and too strong (polycythemia has a higher blood cell count and often includes unsightly blemishes). Of course, with both twins growing up to be healthy adults, the debate of truth in fiction is still a mystery.[citation needed]
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