Twin venous anastomosis

Introduction Twin fetuses are divided into single-oval twins and double-oval twins. The single-oval twins are divided into double amniotic sac double chorion twins, double amniotic sac monochorionic twins and single amniotic sac single chorion twins. Blood circulation includes arteries - arteries, veins - veins, arteries - venous anastomosis. The anastomosis of blood vessels can be divided into superficial and deep layers. Superficial anastomosis refers to the anastomosis of the larger vessels of the fetal surface of the placenta, most of which are direct anastomoses of the arteries and arteries, and a few are direct anastomoses of the veins and veins. In the fetus surface of a few monochorionic twin placentaries, both anastomoses exist. The deep anastomosis is in one or more placental leaflets adjacent to the placenta of the two fetuses. Although it has multiple anastomoses through the capillaries, there is no direct anastomotic or venous anastomosis, but the blood is from a fetus. Flowing to another fetus, Schaty (1900) calls it the "third cycle." A manifestation of twin-transfusion syndrome during twin-venous anastomosis. Twin-blood transfusion syndrome refers to a single-single-single-single-membrane double amniotic sac twin, caused by a fetus (blood donor) in the uterus passing through the placenta unbalanced vascular anastomosis network to deliver blood to another fetus (receiving child) A series of pathophysiological changes and clinical symptoms are serious complications of twin pregnancy or multiple pregnancy, first discovered and proposed by Hedite in 941. The disease can be divided into acute and chronic, which is usually referred to as chronic. The incidence of this disease in monochorionic twins is about 10% to 15%, and the prognosis is poor. If left untreated, the mortality rate can be as high as 80% to 9% (%), and the incidence of neurological diseases in survivors is also high.

Cause

The exact cause of the disease is unclear, and current studies have shown an association with vascular anastomosis between the two fetal placentas. The vascular anastomosis of the two halves of the placenta in the monochorionic twins is ubiquitous. The anastomosis is divided into three types: arterial anastomosis, arterial-venous anastomosis, and venous anastomosis. The anastomotic blood vessels can be located in the shallow or deep layers of the placenta, and they are mutually coincident and compensate each other to maintain the balance of blood circulation between the two fetuses. What exists in the TTTS is the one-way anastomosis between the veins and the veins, but the lack of bidirectional anastomotic branches, which causes the circulation imbalance of the two fetuses. Recent studies have shown that it is possible to relate only to the shallow traffic branch, and the hidden traffic branch in the deep placenta may not cause any clinical symptoms. Cyclical imbalance makes the blood volume of blood donors gradually decrease, resulting in a decrease in urine output and oligohydramnios. In severe cases, the fetus can be wrapped in the amniotic membrane and attached to the side of the uterine wall to form a "attachment" or even a fetal death. At the same time, the blood volume of the blood is gradually increased, resulting in increased urine volume, bladder filling, and excessive amniotic fluid. In severe cases, edema, pleural effusion, ascites, pericardial effusion, and heart failure may occur due to excessive circulating load. Blood donors often have anemia and growth restriction, while recipients show erythrocytosis. After the birth, the blood supply is pale, and the blood is more bloody. Part of the placenta will appear pale relative to the other part. If the neonatal period does not detect and treat severe hypervolemia and hyperviscosity in time, it will be accompanied by heart failure caused by excessive circulating load, and occlusive thrombosis may also occur during this period. Polycythemia can cause severe hyperbilirubinemia and nuclear jaundice. In severe TTTS, changes in umbilical arterial blood flow can be found during ultrasonography. Changes in umbilical arterial blood flow in blood donors are attributed to an increase in placental resistance and a decrease in fetal cerebral arterial resistance. Large placental resistance, the increase in resistance is derived from the oppression of a large amount of amniotic fluid, so changes in umbilical arterial blood flow occur more often and earlier in the donor.

an examination

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System fetal ultrasound examination pregnancy check

Ultrasound can make a preliminary diagnosis of twin-transfusion syndrome before delivery by comparing the determination of single-oval twins, fetal weight assessment, amniotic fluid measurement, umbilical cord and placenta, and the difference between the two fetal viscera. Postpartum examination was confirmed by examination of placenta, hemoglobin level, and body weight difference.

Diagnosis can be divided into prenatal diagnosis and postpartum diagnosis.

1. Prenatal diagnosis: The diagnostic criteria proposed by Quintero et al. are: 1 single chorionic double amniotic sac double sputum (when the chorion is unclear, the twins are: same sex, single placenta, with a thin layer of separation membrane). 2 The difference in amniotic fluid capacity. The blood of the recipients is too much (the maximum vertical dark area of amniotic fluid > 8cm), and the maximum vertical dark area of the amniotic fluid is <2 cm. At present, ultrasound diagnosis is too much water. Too little amniotic fluid has become the gold standard for diagnosis, and the fetal weight and hemoglobin levels are no longer considered.

2. Postpartum diagnosis

1) Fetal examination: At birth, severe TTTS usually shows: 1 fetal birth weight difference is more than 20%; but in the early pregnancy, the fetal weight difference is small; 2 blood supply children pale appearance, blood donors show multiple blood, two The fetal hemoglobin levels differed by >50 g/L, and the red blood cell counts differed by >1 × 10 /L.

2) placenta examination: 1 single placenta, monochorion, double amniotic sac; 2 placenta of blood donor appears pale relative to the placenta of the recipient, 3 diameter of the umbilical cord is larger than the diameter of the umbilical cord of the donor; 4 placental pathology, placenta Perfusion can clearly diagnose the presence or absence of anastomotic vessels in the placenta.

The early diagnosis of TTTS depends on the understanding of its pathogenesis and pathophysiological changes, as well as the monitoring of prenatal ultrasound. Ultrasound can also monitor amniotic fluid and fetal conditions, so in order to reduce mortality, the role of ultrasound examination can not be ignored.

Differential diagnosis

Differential diagnosis of twin-venous anastomosis:

1. The division occurs in the early blastocyst (mulberry period), that is, it splits into two independent fertilized eggs within 3 days after fertilization, forming a double amniotic sac double chorion double placenta.

2, the division occurs in the late blastocyst, that is, 4 to 8 days after fertilization, the formation of a single amniotic membrane of the double amniotic sac.

3, the split occurs after the formation of the amniotic sac, that is, 9 to 13 days, the formation of a single amniotic sac monochorionic single placenta.

4, the split occurred after the 13th, forming different levels, different forms of joint children.

Ultrasound can make a preliminary diagnosis of twin-transfusion syndrome before delivery by comparing the determination of single-oval twins, fetal weight assessment, amniotic fluid measurement, umbilical cord and placenta, and the difference between the two fetal viscera. Postpartum examination was confirmed by examination of placenta, hemoglobin level, and body weight difference.

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