[Overview] Twin-twin transfusion syndrome (TTTS) is a complication that occurs specifically in monochorionic twins. In most monochorionic twins, transfusion via anastomotic vessels is a continuous but balanced phenomenon, but in 10-15% of monochorionic twins, an imbalance in the development of the vascular network leads to TTTS, which often occurs between 15 and 26 weeks of age. TTTS occurs through the unidirectional transport of blood from the arteries to the veins via the arterial and venous anastomotic branches of the intertransplacental space, whereby one fetus is the donor and the other is the recipient. The other fetus becomes a recipient (recipient), resulting in the donor fetus being light in weight, small in length, anemic, dehydrated, urinating less, having less amniotic fluid, having insufficient blood volume, and eventually dying from ischemia; while the recipient fetus, due to excess blood volume, has a hypertrophied heart, an enlarged liver and kidneys, gains too much weight too quickly, develops congestive heart failure, develops fetal edema, has excess amniotic fluid, and eventually dies of congestive heart failure as well. Fetal death in utero occurs in 80-100% of TTTS if left untreated during pregnancy. Current research suggests that in addition to the interplacental arteriovenous anastomotic traffic branch causing TTTS, placental hemodynamics and hormones such as the renin-angiotensin system also play a role in the development of TTTS. Before the use of ultrasound in clinical diagnosis, TTTS could only be diagnosed by careful examination of the placental vessels and observation of placental vascular traffic based on the inconsistent growth of the fetus at the time of delivery. With the rapid development of fetal medicine, TTTS can not only be diagnosed in the prenatal period, but also can be further treated, but there will still be near and far-term complications and neonatal neurological sequelae. [Diagnostic criteria] 1, early and mid-gestation twin pregnancy chorionic diagnosis (1) early pregnancy ultrasound monitoring of twin fetuses if there are two separate gestational sacs, for the two ovarian twins; (2) early and mid-pregnancy ultrasound monitoring of a chorionic villus cavity with two amniotic sacs, amniotic membrane and chorionic villous membrane between the “T” shaped structure of single chorionic villus twins; the “λ” structure; the “T” shaped structure of single chorionic villus twins; and the “λ” structure of single chorionic villus twins; and the “λ” structure. “(3) Ultrasound monitoring of the presence of two placentas and a layer of septum 2mm or thicker can assist in the diagnosis of dual chorionic villous twins; (4) the sex of the twin fetuses is different for dizygotic twins. 2, TTTS diagnostic criteria: (1) two fetuses of the same sex, single placenta; (2) the growth of the two fetuses is inconsistent, the estimated difference in weight is more than 20%, abdominal circumference is more than 20mm, the difference between acute cases may not be obvious; (3) the donor child amniotic fluid is too small: ultrasound maximal amniotic fluid level segment ≤ 2cm; (4) the recipient fetus amniotic fluid is too large: ultrasound maximal amniotic fluid level segment ≥ 8cm before the twentieth week of gestation, 20 to 26 weeks of ultrasound amniotic fluid level segment ≥ 10cm. (5) Difference in hemoglobin between two fetuses ≥5g/L. Diagnosis can be confirmed by invasive prenatal diagnosis of umbilical cord puncture to obtain fetal blood samples. (6) Fetal ultrasound Doppler abnormalities: loss of end-diastolic flow or reflux in the umbilical artery of the donor child at stage III, or abnormalities in the Doppler images of the veins of the recipient child, such as intraventricular reflux or umbilical vein pulsatile flow. 3.Postnatal diagnosis of TTTS Newborns of the same sex, weight difference >20%, same blood type, hemoglobin difference >5g/L, pale and anemic appearance of the donor child, and the recipient child has a reddish face and bruxism. The two placentas are fused, and some of the placental lobules are shared in the middle, with tiny blood vessels connected, or with larger blood vessels communicating, and amniotic separation can be seen in the middle. 4.TTTS staging diagnosis Traditional Quintero staging: Stage I: too much amniotic fluid or too little amniotic fluid, blood-supplying fetal bladder can be seen. Stage II: the donor fetal bladder is not filled. Stage III: Loss of end-diastolic flow or regurgitation of the umbilical artery in the donor fetus or abnormal Doppler images of the veins of the recipient fetus, such as intraventricular regurgitation or umbilical vein pulsatile flow. Stage IV: fetal hydrops. Stage V: death of one or both fetuses. 5. Differential diagnosis: Differential diagnosis from twin fetuses with inconsistent growth, see related chapters. Treatment plan] In the middle and late stages of pregnancy, for the diagnosis of uncomplicated monochorionic twin fetuses, ultrasound examination of fetal health status should be performed every 3-4 weeks. Once the diagnosis of TTTS is made, ultrasound examinations of fetal status need to be performed every 2 weeks or even every 1 week. Since it often occurs before 28 weeks of gestation and is prone to intrauterine fetal death and preterm delivery of the first fetus, it is necessary to transfer the pregnant woman to a tertiary care institution. 1.Expectant therapy For patients with early TTTS around 28 weeks of gestation (before Quintero stage II) and for patients with uncertain diagnosis and no conditions for surgery can be followed up regularly to prolong the pregnancy and terminate it at the right time, and strive for viable newborns. 2.Treatment of TTTS in mid-pregnancy: applicable to pregnant women with TTTS in all stages. (1) Amniocentesis reduction: to prevent preterm labor and correct hemodynamic imbalance. (2) Amniotic diaphragm perforation: laser perforation of the amniotic diaphragm or puncture needle perforation under fetoscopy. (3) Fetoscopic laser electrocoagulation vascular anastomosis: a more risky procedure than amniotic fluid reduction, which must be undertaken by a physician with specialized training. (4) Obstructed umbilical cord selective fetal reduction: It has been suggested for TTTS stages III and IV. Complications of TTTS treatment (1) Intraoperative complications: leakage of amniotic fluid, hemorrhage, loss of instruments in the amniotic cavity, infection, detachment of membranes, placental abruption, loss of fetal heart, miscarriage, incomplete blockage of vascular traffic branches, or omission, accidental injury to normal blood vessels. (2) Proximal and distant complications: disappearance of both fetal hearts successively a few hours after the operation, miscarriage, especially in patients with end-diastolic disappearance or regurgitation of the umbilical artery S/D in stage III TTTS, high rate of near-term miscarriage; preterm labor; premature rupture of membranes; and in the distant stage, amniotic fluid, fetal growth restriction, and intrauterine foetal death, etc., may also occur. (3) Neurological sequelae of newborns: surviving children have different degrees of neurological sequelae and intellectual impairment, which is related to whether the fetus at the time of surgery is severely ischemic and hypoxic, the earlier the surgery, the fewer sequelae. 4, close follow-up after surgery to prevent miscarriage, preterm labor and intrauterine fetal death. 5.Timely termination of pregnancy and mode of delivery Applicable to patients with late TTTS after 28 weeks of gestation, mode of delivery is the same as obstetric treatment, the maturity of fetal lungs needs to be evaluated before termination of pregnancy and fetal lung maturity needs to be promoted. 6.After the birth of the newborn, obstetrics, neonatology and anesthesiology will collaborate to carry out timely and necessary resuscitation, and transfer to NICU for further treatment according to the situation. 【Evaluation of efficacy】 The diagnosis and treatment of TTTS requires high professional and technical ability of medical institutions, and a team of obstetricians, ultrasonographers, maternal-fetal medicine specialists, anesthesiologists, and nursing specialists should be organized to establish a regional fetal medicine center and formulate therapeutic measures. The therapeutic approach to TTTS in mid-pregnancy carries a risk of preterm labor, miscarriage and intrauterine fetal death as well as neurological sequelae for the fetus. The primary criterion for efficacy assessment is survival of at least one fetus to the sixth month of gestation, and the secondary criterion is the absence of neurologic injury in the surviving fetus; or delivery after TTTS treatment, with survival of both fetuses or at least one neonate for 28 days as the gold standard for efficacy of treatment, according to which efficacy of surgical treatment can be compared globally. B. Single Intrauterine Fetal Demise (sIUFD) [Overview] Single Intrauterine Fetal Demise (sIUFD) is a complication specific to twin fetuses, and compared with intrauterine foetal death in singleton pregnancies, it is different in terms of etiology, maternal and infant conditions, and the impact of the fetus on the fetus, and the risk is highest for twins of the same sex, and the risk is higher for twins with different growth, different growth, and different fetal outcomes. is highest, and the risk of stillbirth is also increased by incompatible twin growth, severe malformations, and TTTS; the risk of intrauterine fetal death of one fetus and death of the other surviving fetus is six times higher in same-sex twins than in opposite-sex twins. Death of one fetus early in pregnancy is a disappearing twin, and a stillborn fetus in the middle trimester will appear as a papery fetus. Death of one fetus in late pregnancy causes coagulopathy in the mother, but is rarely reported in the literature and may be associated with delivery soon after a few weeks. In twin sIUFD, the risk of neurologic anomalies and preterm labor is significantly increased in the surviving fetus, and the risk of neurologic anomalies is significantly higher in monochorionic twin fetuses than in bichorionic twin fetuses. Diagnostic criteria] 1, most of the fetal death occurs in early pregnancy, the diagnosis is mostly based on the initial ultrasound examination suggests two gestational sacs, and then found that one gestational sac disappeared, when the discovery of confirmed fetal remnants or subsequent ultrasound examination confirms that a fetal death or the disappearance of one of the previously viable fetuses should be diagnosed as sIUFD. 2, late pregnancy: ultrasound monitoring of the twins of the fetal heart disappeared in one of the twin fetuses. [Treatment plan] 1, expectant therapy Depending on the chorionicity of the twin fetuses and the risk of surviving fetuses, to prevent the occurrence of preterm labor and miscarriage. Double chorionic villous twin one fetus died when the other surviving fetus is in good condition, it is not necessary to take immediate treatment measures, regular fetal monitoring and biophysical condition assessment of the surviving fetus, monitoring the growth and development of the surviving fetus. Monochorionic twin fetuses, when one fetus dies, the other surviving fetus is in good condition, regular ultrasound Doppler monitoring of umbilical cord blood flow and middle cerebral artery blood flow should be carried out, and vaginal ultrasound and MRI can also be used to check the brain damage of the surviving fetus in the hospitals that have the conditions. Termination of pregnancy (1) In late pregnancy, if the fetus is viable but premature, glucocorticoid therapy should be given to promote the maturation of the fetal lungs. (2) Fetal death of one fetus at full term: generally, termination of pregnancy should be chosen to save the other fetus without expectant treatment. The choice of mode of delivery should be based on the mother’s condition as well as the size and position of the fetus and whether it can tolerate vaginal delivery. 3. Monitor the mother’s coagulation status before termination of pregnancy. After birth, the newborn should be transferred to NICU for further treatment according to the situation. [Assessment of efficacy] The surviving fetus is closely monitored, and the newborn is born alive without near- or long-term complications. Third, the uneven development of twins (twin growth inconsistency) 【Overview】 Twin growth inconsistency (discordant growth twin) is a unique complication of twin pregnancies, the difference between the weight of the newborn after birth > 20% can be used as a diagnostic criterion. It can be divided into double chorionic villus twin growth inconsistency and single chorionic villus twin growth inconsistency, size inconsistency is often defined in terms of the larger fetus in the twin as the criterion, the greater the difference in inconsistency the higher the incidence of its serious illnesses, and the earlier the occurrence of its sequelae the more serious. Dystocia usually occurs at the end of the middle and beginning of the second trimester and is often disproportionate, and may occur in the early trimester when the smaller fetus may have large malformations. The likelihood of both fetuses being small for gestational age (SGA) is twice as high in monochorionic as in dichorionic twins. It has been reported that growth discrepancy in bichorionic twins is associated with inadequate placental perfusion, while growth discrepancy in monochorionic twins is associated with placental hemodynamic imbalance. The risk of growth discrepancy is similar to that of monochorionic twins, and the rate of neonatal morbidity and mortality after birth is increased. Diagnostic criteria] The diagnosis of twin growth discrepancy is based on the measurement of various fetal parameters, and the diagnosis of twin growth discrepancy after birth is more conclusive. Clinical manifestations The difference in weight of newborns after birth is more than 20%. (1) Prenatal ultrasound monitoring of the difference in abdominal circumference between the two fetuses is 20mm. (2) Prenatal ultrasound monitoring of the difference in fetal weight is >20%, fetal weight is based on fetal biparietal diameter and abdominal circumference or femur length and abdominal circumference measurements entered into the computer to assess, which can assist in the diagnosis. (3) Ultrasound Doppler measurement of the difference between fetal umbilical artery flow ratio (S/D) >15% and diastolic regurgitation can assist in diagnosis. (1) Inconsistent growth of two fetuses of appropriate gestational age. (2) Inconsistent growth of two fetuses of less than gestational age. (3) Inconsistent growth of a fetus of gestational age and a fetus of less than gestational age. Differential diagnosis Differential from TTTS. (1) A growth-restricted fetus with incongruent growth looks like an “adherent fetus” because of low amniotic fluid, but a normal-growing fetus has a normal amniotic fluid volume. In TTTS, the recipient fetus has too much amniotic fluid and the donor fetus has too little amniotic fluid. (2) TTTS can be differentiated from growth discrepancy by indicators such as bladder filling and cardiac changes in both fetuses. [Treatment plan] Close monitoring should be done during pregnancy to prevent intrauterine fetal death and to choose an appropriate time to terminate the pregnancy. 1.Monitoring during pregnancy (1) Ultrasound evaluation of fetal growth and development: ① Ultrasound evaluation is recommended every 3-4 weeks in the middle and late stages of twin pregnancies. Evaluation content for ultrasound monitoring fetal abdominal circumference, biparietal diameter, head circumference, femur length, amniotic fluid volume and fetal weight, and at the same time monitoring the umbilical artery blood flow S / D ratio changes. (2) If the growth of twin fetuses is inconsistent or there is S/D abnormality, closer monitoring should be carried out according to the condition. (2) Strengthen the monitoring of fetal heart rate and biophysical score to evaluate whether the fetal condition is good. (2) Terminate the pregnancy at the right time ①The inconsistent growth of twin fetuses does not require routine interventional termination of pregnancy. ② late pregnancy if intrauterine fetal hypoxia and other obstetric indications of the need to terminate the pregnancy with obstetric treatment, termination of pregnancy before the need to clarify the situation of fetal lung maturity. Evaluation of the efficacy of the treatment] The growth and development of the fetus is regularly evaluated in the middle and late stages of pregnancy, and the pregnancy is terminated at the appropriate time, and the newborn is born healthy without near or far-term complications. One twin malformation includes structural anomalies, chromosomal abnormalities, and monochorionic twin-specific malformations twin reverse arterial perfusion (TRAP). The incidence of structural abnormalities in one twin is the same per fetus as in monochorionic twins, the risk of chromosomal malformations in one twin can be calculated by adding the age-related risks (e.g., the risk for a 40-year-old woman is 1/100 + 1/100 = 1/50), the incidence of structural abnormalities in one twin is 2-3 times higher per fetus than in monochorionic twins, and chromosome malformations are rare in one twin, which is referred to as the different karyotypes of monochorionic twins. This rare phenomenon is called monozygotic twins with different karyotypes. Abnormalities in one of the twins with excess amniotic fluid and death can cause preterm delivery of the other fetus, and abnormalities in one of the monochorionic twins can cause preterm delivery of the other fetus, brain damage, and intrauterine death, with the majority of abnormalities detected in the second trimester. Fetal karyotype determination is performed by invasive tests amniocentesis or chorionic villus biopsy (CVS), which are technically demanding and therefore usually recommended to be performed in prenatal diagnostic centers of tertiary health care institutions. The choice of invasive tests depends on the risks associated with this operation and the accuracy of the results obtained from the fetus and the technique, the rate of miscarriage being currently inexact. Either amniocentesis or chorionic villus biopsy (CVS) may be used in dizygotic twins, usually sampling both fetuses. Amniocentesis is preferred in monozygotic twins because CVS rarely diagnoses monozygotic twins with different karyotypes. 【Treatment plan】 1. Expectant treatment When the malformation of one of the twin fetuses does not affect the health of the normal fetus, the growth and development of the fetus is regularly monitored. 2.Selective fetal reduction and selective termination of pregnancy: in the early and middle stages of pregnancy, it must be performed in qualified third-level medical institutions. Indications for surgery: the existence of conditions that threaten the health of the normal fetus. If one of the twin fetuses is anencephalic, causing progressive pathologic amniotic fluid excess, which can lead to preterm delivery of the other fetus. (1) Selective fetal reduction or elective termination of pregnancy in bichorionic twins is performed by intracardiac or intraspinal injection of potassium chloride under continuous ultrasound monitoring. It is extremely important to identify the target fetus to be killed by differentiating between the sexes, identifying obvious structural abnormalities, placental positioning, and umbilical cord attachment. (2) Monochorionic twin fetuses It is uncertain which method of selective fetal reduction is best. Selective termination of pregnancy using laser/bipolar electrocoagulation occlusion of the umbilical cord or umbilical cord ligation is recommended in fetal medicine centers that perform intrauterine fetal therapy. (3) Complications of the procedure: The risks of elective abortion or elective termination of pregnancy are miscarriage, preterm labor, maternal infection, hemorrhage during pregnancy, and diffuse intravascular coagulation. 3. Monitor the condition of the surviving fetus and the mother’s well-being after elective fetal reduction or elective termination of pregnancy. Termination of pregnancy after 28 weeks of gestation should be handled in the same way as obstetric indications. Preventing postpartum hemorrhage and timely use of uterotonics after delivery. After birth, transfer the newborn to NICU for further treatment according to the situation. Assessment of therapeutic efficacy】 Closely monitor the growth and safety of the fetus in the uterus, and the healthy fetus is born alive without near and far-term complications.