Twin pregnancy

Introduction to twin pregnancy Twin pregnancy is generally more serious in early pregnancy, prone to iron deficiency anemia, and is also prone to pregnancy-induced hypertension, polyhydramnios, fetal malformation and placenta previa, premature rupture of membranes and premature delivery in the third trimester, prone to childbirth during childbirth Weakness, dystocia and postpartum hemorrhage. A family history of multiple pregnancies, which received ovulation induction therapy before pregnancy. The size of the uterus is significantly larger than the single pregnancy in the same month. The abdomen can touch two fetal heads or multiple small limbs, or the fetal head is small, which is not proportional to the size of the uterus. Two fetal heart sounds can be heard in different parts, and the fetal heart rate is inconsistent. , or two fetal heart sounds are separated by a soundless zone. Twin pregnancy is more common, the incidence of twins is reported in China about 16.1%, and twins are divided into two categories. 1. Double-oval twins, that is, twins formed by fertilization of two eggs respectively, generally two or more eggs are matured at the same ovulation period, and two eggs are fertilized. 2. Monozygotic twins (identical twins) are divided by one fertilized egg and become two fetuses called single-oval twins. The divided embryos can form independent fetuses except for a very small number. These twins account for about 30% of the total number of twins, and are generally constant at around 1:255. In general, the maternal changes in pregnant women are more pronounced than those in singletons. The most important thing is that the maternal blood volume increases by 500ml more than a single child, but it is interesting to note that the average postpartum blood loss in 25 pairs of twins is 935ml. More than 500ml more than a single fetus, due to the sharp increase in blood volume, and the development of two fetuses, the need for iron and folic acid has increased dramatically, so the mother is more prone to anemia. Veille et al. (1985) estimated the heart of twin pregnant women with cardiac ultrasound. Function, compared with a single fetus, cardiac output increased, but the ventricular volume at the end of diastole is still the same, the increase in cardiac output is related to the increase in heart rate and the increase in stroke volume. basic knowledge The proportion of sickness: 0.4% Susceptible population: pregnant women Mode of infection: non-infectious Complications: premature labor anemia, pregnancy-induced hypertension, polyhydramnios

Cause of twin pregnancy

(1) Causes of the disease

The occurrence of twin pregnancies is related to race, age, maternal parity, genetic factors, nutrition, season, and serum gonadotropin levels in women. In addition, the use of ovulation induction drugs and assisted reproductive technology has also increased the incidence of multiple pregnancies.

1. The incidence of multiple pregnancies between races and ethnicities varies greatly. The incidence of twin pregnancies in Nigeria is the highest. In 1969, the incidence of twins in Ibaban was as high as 50, and in the United States, 12. England and Wales are 11, while Japan is the lowest with 6.5.

2. Epidemiological data of genetic factors indicate that the frequency of twins in a family with a family history of twins is 4 to 7 times higher than that of the general, and there is no familial tendency in single-oval twins, while twins are genetically related. The twins are inherited by the mother's female inheritance, the father's role is less or no effect, and some people have a familial study on women who have given births twice or more, and found that these women are themselves one of the twins. 4.5, 5.5 of the sisters have given birth to twins, and the children of their brothers are 4.5 twins.

3. The incidence of twins and twins in pregnant women increases with the age of pregnant women. The incidence of double-oval twins in women aged 15-19 years is 2.5, while in women aged 30-40, it rises to 11.5. The incidence of egg twins is not obvious. The literature reports that the incidence of single-oval twins in women under 20 years old is 3, and only rises to 4.5 in those over 40 years old.

4. Pregnancy and maternity of pregnant women Many scholars believe that women who give birth more than three times are high-risk groups with multiple pregnancies. In the fourth and above, the incidence of twins has increased significantly. In recent years, women in western developed countries have also implemented family planning. Women with high parity have been significantly reduced, and the incidence of twins has decreased slightly.

5. Nutritional animal experiments have shown that increasing nutrition can increase the incidence of twins. France had a twin prevalence of 7.1 before the Second World War and 3.7 in wartime.

6. Environmental factors have shown that continuous sunlight can enhance the thalamic stimulation of the pituitary, increase the level of gonadotropin in women, and increase the incidence of multiple pregnancies. In some parts of northern Finland, the incidence of multiple pregnancies is highest in July.

7. The occurrence of serum gonadotropin levels in twins is closely related to the level of serum gonadotropin in pregnant women. In Nigerian women with the highest incidence of double-oval twins, gonadotropin levels have been measured. Japanese women with the lowest incidence of twins have lower levels of gonadotropins.

8. Ovulation-promoting drugs In women with infertility, the use of ovulation-promoting drugs can cause multiple primordial follicles to develop at the same time, mature, easily lead to multiple pregnancy, according to the detection of early pregnancy of B-ultrasound, the application of human postmenopausal gonadotropin (HMG) The chance of twin births will increase by 20% to 40%, and the application of chlorophenolamine CC will increase by 5% to 10%.

9. In vitro fertilization Since the in vitro fertilization study, the incidence of multiple pregnancies has increased significantly as a result of each input of more than three fertilized eggs in the uterine cavity.

(two) pathogenesis

In general, the maternal changes in pregnant women are more pronounced than those in singletons. The most important thing is that the maternal blood volume increases by 500ml more than a single child, but it is interesting to note that the average postpartum blood loss in 25 pairs of twins is 935ml. More than 500ml more than a single fetus, due to the sharp increase in blood volume, and the development of two fetuses, the need for iron and folic acid has increased dramatically, so the mother is more prone to anemia. Veille et al. (1985) estimated the heart of twin pregnant women with cardiac ultrasound. Function, compared with a single fetus, cardiac output increased, but the ventricular volume at the end of diastole is still the same, the increase in cardiac output is related to the increase in heart rate and the increase in stroke volume.

Another maternal change is that the volume and tension of the uterus in a twin pregnancy is significantly increased, its capacity will increase by 10L or more, and the weight will increase by at least 9kg (20Ib). Especially in single-oval twins, the amount of amniotic fluid can increase rapidly. Excessive acute amniotic fluid, in addition to oppression of the abdominal organs, and even displacement, may have diaphragmatic elevation, renal damage, Quigley and Cruikshank (1977) reported two cases of twin pregnancy with acute polyhydramnios, nitrogen Hememia and oliguria.

The main effect on the fetus is in weight, fetal growth restriction and premature birth make the fetus weight lighter. Compared with singleton, before the 28th week of pregnancy, the twin fetus is slightly lower than the single fetus, but the difference Not big, after 28 weeks of pregnancy, the difference in body weight is increasingly significant. After 34 to 35 weeks, the separation of body weight is particularly obvious, but it is meaningful that the two fetuses at this stage are added together and the body weight is often 4000~ 5000g.

Regarding the weight of the two fetuses, the difference is generally small, but when the twin-child transfusion syndrome occurs in the single-oval twins, the body weight often differs by 500g or more. As for the double-oval twins, the body weight can also vary greatly. For example, in a case of a twin in Parkland Hospital, a female newborn is 2300g, a suitable age, and a male newborn is 785g, both of which survive. In the later growth process, the latter always lags behind the former.

Twin pregnancy prevention

Early detection, strengthen pregnancy tests, pay attention to its complications. Preventive work begins with the details of life.

Twin pregnancy complications Complications, premature anaemia, pregnancy-induced hypertension, polyhydramnios

Maternal complications

(1) Premature birth: Due to the excessive expansion of the uterus of the twins, the incidence of premature birth is inevitable. As early as 1958, Mckeown reported that the average pregnancy of twins was 260 days, and half of the twins were <2500g. Premature birth is naturally occurring, and some occur after premature rupture of membranes. The incidence of premature rupture of membranes in single-oval twins is higher than that of double-oval twins, but the cause is unknown. Because of the high incidence of fetal position in twins, it is broken. The incidence of postoperative umbilical cord prolapse is also higher than that of singleton. Preterm birth is the main cause of twin mortality and neonatal prevalence. Recently, Pons (1998) reported that the average gestational age of 842 twins was 36.2 weeks. The premature birth rate is 45.96%, and the perinatal mortality rate is 39.2. The main cause of death is still premature birth. Compared with singleton, twin pregnancy itself does not cause more harm to the fetus than single pregnancy. The incidence of twin preterm birth is much higher than that of a single child, so it is the main danger.

(2) Anemia: As mentioned above, anemia in twin pregnancy is about 40%, mainly because the iron and folic acid reserves are insufficient to cope with the growth needs of the two fetuses.

(3) Pregnancy-induced hypertension: Pregnancy-induced hypertension is one of the main complications of twins. The incidence is 3 to 5 times higher than that of single-pregnant pregnancy. It is especially common in primipara, which develops into pregnancy-induced hypertension before 37 weeks of gestation. About 70%, and single pregnancy is only 6% to 8%, the time of occurrence is earlier than single pregnancy, and the condition is heavy, easy to develop into eclampsia, the incidence of small for gestational age is also increased, in addition, there is ICP People are also prone to pregnancy-induced hypertension.

(4) Excessive amniotic fluid: In twin pregnancy, as early as a single pregnancy, polyhydramnios is often seen, but it gradually decreases. The final development of polyhydramnios is about 12%. Acute amniotic fluid is excessive. It is more common in single-oval twins and often occurs before it can survive, so it is a great threat to the fetus.

(5) Intrahepatic cholestasis of pregnancy (ICP): ICP is one of the common complications of pregnancy in pregnant women in China. The cause of the disease is related to estrogen. The level of estrogen in pregnancy is abnormally increased. In one placenta, the level of estrogen is more obvious. The main symptoms are itching, elevated liver enzymes or elevated bilirubin, and jaundice. The main threat to the fetus is premature birth and intrauterine asphyxia, resulting in sudden death.

(6) abortion: the abortion rate of twins is higher than singleton. In early pregnancy, the diagnosis of twins by B-ultrasound is about 20% spontaneous abortion before 14 weeks of pregnancy, which is 2 to 3 times of single pregnancy, abortion may It is associated with embryonic malformation, abnormal placental development, placental blood circulation disorder, and relatively narrow uterine volume.

2. Fetal complications

(1) Fetal growth restriction: fetal growth restriction and premature birth are the two major causes of low birth weight twins. Fetal growth restriction must rely on B-ultrasound diagnosis, often from the second trimester of pregnancy, the fetus has growth restriction. Trends, the incidence of fetal growth restriction in twin pregnancies is 12% to 34%, and its incidence and severity increase with the increase of gestational age, while single-oval twins are more obvious than double-oval twins, especially Is associated with twin-transfusion syndrome, the weight difference between the two fetuses is greater; those with pregnancy-induced hypertension are also prone to fetal growth restriction.

(2) Twin-twin transfusion syndrome (TTTs): TTTs are a serious complication in twin pregnancy, and the incidence is not accurate. This may be related to people's knowledge. Reported that the incidence rate is 4% to 35%, the perinatal mortality rate of TTTs is extremely high, pathological basis and clinical manifestations: the vast majority of TTTs occur in the double amniotic sac monochorionic twin, its pathogenesis and two fetuses The placental vascular anastomosis is closely related. The lesions of TTTs are mainly in the deep part of the villus in the fusion site of the two placenta. Although the vascular anastomosis can pass through the capillary, there is no direct arteriovenous anastomosis, but the blood is always From one fetus to another, in most single-oval twins, the arteriovenous anastomosis of the two placenta in these placental lobes has an equal distribution of blood flow, resulting in a flow from a fetus in unit time. The blood flow of the fetus is equivalent to the blood flow of the fetus to the fetus, so the rate of fetal development is similar, but when the vascular anastomosis is uneven, the unit When the blood flow to the fetus is higher than the blood flow to the fetus, the fetus becomes a donor, and the fetus becomes a recipient. The imbalance of blood volume leads to a series of changes, the blood supply of TTTs. As the blood is continuously delivered to the recipient, it is gradually in low blood volume, anemia, small in size, light in weight, similar to growth restriction, and at the same time due to anemia, red blood cell reduction, low hematocrit, and possibly mild edema Of course, blood donors also increase the ability to make red blood cells due to anemia, but often because of low blood volume, oliguria, oligohydramnios occurs, the recipients of the blood are large, and their liver, kidney, pancreas and adrenal glands are enlarged, and the blood cell is packed. Significantly higher than the blood supply, high blood volume, hyperbilirubinemia, high blood volume, increased fetal urine volume, resulting in excessive amniotic fluid. Recently, Nageotte et al found that aTTP in the recipients of TTTs Increased blood supply, atrial peptide hormone is a peptide hormone secreted by special cells of the atria, which can promote the discharge of water and electrolytes from the kidneys, which is one of the causes of excessive amniotic fluid, the incidence of TTTs. In the middle, the umbilical cord-like attachment may also be one of the causes of the disease, because the umbilical cord attached to the sail is fixed on the uterine wall for a long period of time and is easily compressed, so that a fetal blood flow is reduced and TTTs occur, in the twins. The unintentional malformation is a rare form of malformation, often accompanied by TTTs, which often coexist with a single umbilical artery. It often grows with the blood supply of another fetus, so the recipient is often accompanied by edema and polyhydramnios. The normal fetus is a donor, the individual is small and anemia, and the amniotic fluid is too small. The diagnosis of TTTs: prenatal diagnosis: B-ultrasound is an important means of prenatal diagnosis of TTTs.

1 The diagnosis of single-oval twins is a prerequisite. Barss believes that a single placenta, a fetus of the same sex, and a fine mediastinum between the fetus can be determined to have a higher diagnostic accuracy for a single chorionic twin, Nores et al. (1997). ) Reporting the ratio of male to female in TTTs cases, women have a clear advantage, the reasons are yet to be determined.

2 fetal weight difference and fetal performance: Many scholars believe that if the abdominal circumference is 20mm, the weight difference is 20%, another fetus is stunted, and because the amniotic fluid is too small, it is less moving, showing a rigid state, also a kind of TTTs. Special phenomenon.

3 The difference in amniotic fluid: the presence of polyhydramnios and oligohydramnios is one of the important conditions for the diagnosis of TTTs. Observing the fetal bladder filling and estimating the fetal urine output is also one of the diagnostic methods.

4 Differences in umbilical cord: In the B-ultrasound, the umbilical cord of the recipient is larger than that of the donor, and sometimes the umbilical cord of the recipient is accompanied by a single umbilical artery.

5 Organ difference: Lachapalle (1997) in 5 cases of twins confirmed as TTTs after delivery, B-ultrasound during pregnancy showed that the ventricular wall of the recipient was thickened, the left ventricle of the donor was shortened, and the cardiac output was Both increased significantly, indicating that the heart activity is in an excessive state, while the latter is more helpful for diagnosis. Robert et al. (1997) found that the length of the liver of the recipient and the donor was significantly greater than that of the double chorion twin as the control group. Diagnostic value.

6 umbilical puncture: Some scholars believe that puncture of the umbilical blood vessels under the guidance of B-ultrasound to obtain blood samples can be of great help in the diagnosis of TTTs, one can diagnose single-oval twins, the second can measure the difference in hemoglobin levels and the anemia state of the fetus, but the method There is some damage, so there are not many reporters.

Postpartum diagnosis:

1 Placenta: The placenta of the blood supply is pale, edematous and atrophic. Because of the oligohydramnios, there is amnion nodules on the amniotic membrane, and the placenta is red and congested.

2 Hemoglobin level: Generally, the hemoglobin level of the recipients of TTTs and the blood donors differs by more than 50g/L, and even 276g/L is 78g/L. Therefore, the difference is 50g/L, but there is also a difference of not more than 5g.

3 Weight difference: The standard for neonatal weight difference is generally set at 20%, but it is also considered to be 15%.

Prognosis and management of TTTs: The prognosis of untreated TTTs is poor, the earlier TTTs appear, the worse the prognosis. If not treated, the perinatal mortality rate is almost 100%, such as diagnosis and treatment before 28 weeks. The mortality rate of children is still between 20% and 45%. There are several treatment methods for prenatal diagnosis of TTTs:

1 amniotic fluid excessive amniocentesis.

2 selective sterilization.

3 When the affected children have persistent heart failure, the cardiotonic and pericardial punctures are given.

4 The use of laser to block TTTs between the two placenta vascular anastomotic branches to treat TTTs between the two placenta vascular anastomosis, this method is a promising method.

(3) Respiratory stress syndrome (RDS): Although the RDS of twin pregnancy with the same gestational age is not increased compared with the single fetus, the incidence of preterm birth due to twin pregnancy is high, very low and extremely The incidence of low birth weight children is also bound to increase, so RDS is an important complication of twin pregnancies, may be premature birth, or should be prevented when there are signs of premature birth.

(4) Fetal malformation: the twin malformation is twice as large as the single fetal malformation, while the single-oval twin deformity is 22 times that of the double-oval twin. According to Baldwin et al. (1990), 14 articles, 112,384 doubles were reviewed and studied. Fetal, four points of advice on twin malformations: First, twins are 1.2 to 2 times more common than singletons; second, in the same gender or in single-oval twins, single-chorionic twins The incidence rate is higher; thirdly, in 80% to 90% of twin treads, the structural abnormalities are inconsistent, although the coincidence rate of monozygous twins is consistent, but not related to monozygous or doublet; Most malformations are cardiac malformations, neural tube defects, facial fissures, digestive tract malformations, anterior abdominal wall malformations including cloaca and bladder eversion, but some deformities are unique to twins, such as conjoined twins, no heart malformations, fetal inner tubes, etc. .

1 conjoined twins: as in the case of a single-oved twin fertilized egg splitting into two embryos occurring 13 days after fertilization, the two germinal centers on the blastoderm are not completely separated, allowing the two embryos to share the intermediate region However, they are not completely separated, resulting in a twin twins, with an incidence of 1:50,000 to 1:100,000.

2 acardius (acardius): no heart malformation is a type of malformation without a heart. In recent years, many reports are rare in single-oval twins, the incidence rate is 1:30,000 to 1:40, The reason is unknown. In this kind of twin placenta, it is common to see at least one artery and one vein-venous communication between the normal fetus and the placenta of the unintentional fetus. Therefore, the heartless deformity relies on the power of the normal fetal heart to reverse the blood. If you survive by perfusion, the blood oxygen and nutrients in the reverse blood flow are low. In the early pregnancy, the normal fetus has a strong heart function, and the other fetal heart stops developing. Finally, the deformed, unintentional umbilical cord often merges with the umbilical cord. Umbilical artery, because the normal fetus has to bear the blood supply of two fetuses, its load is too heavy, if not treated in time, normal fetus can develop chronic hypertension, heart failure and death.

3 parasitic fetus: in the blastocyst stage, the cell mass division is asymmetric, and the poorly developed inner cell mass is anastomosed with the normal developing embryo yolk sac vein, and is gradually entrapped into the body, becoming a parasitic fetus, or a fetal inner tube, and most of the parasitic fetus. Located in the posterior retroperitoneal region of the upper fetus of the normal fetus, the connective tissue on the surface of the carcass, the development of the carcass is incomplete, there are hypoplastic vertebral columns, ribs, pelvis and limbs, and sometimes some of the skull and visceral insufficiency.

(5) The normal birth of one child in a twin is a mole: it is not uncommon. It has been reported in the literature, but the incidence of twins has increased in recent years, and similar reports have increased. The author believes that the risk of complete moles combined with pregnancy is The possibility of bleeding increases and later develops into a persistent trophoblastic disease.

(6) One-child chromosomal abnormality in twins: The inconsistency of chromosomes in single-oval twins is a very rare phenomenon, but it is reported as such.

(7) Abnormal fetal position: Compared with a single fetus, the abnormal fetal position of the twin fetus is significantly increased. Only the head-to-head of the two fetal fetuses in the twin fetus is completely normal, accounting for only the statistics of various twins. 38% to 42%, and the first place's fetal position is 18% to 25%, and there are still many horizontal positions. After the first baby is delivered, the second child's fetal position is still abnormal. It accounts for a high proportion, so if the midwife lacks experience, he may make a mistake here.

Twin pregnancy symptoms Common symptoms Twin fetal vein anastomosis Fetal intrauterine asphyxia menopause and galactorrhea weight gain Physiological changes during pregnancy Fetal movement Frequent dyspnea Early pregnancy response Ductile varicose

Clinical manifestations of early pregnancy response, uterine enlargement and pregnancy months do not match, excessive weight gain, frequent fetal movements, increased uterine bulge due to excessive uterine uterus during the third trimester, and increased diaphragmatic pressure and cardiopulmonary dyspnea, due to venous return obstruction, High edema and varicose veins can occur in the lower extremities and perineum.

Abdominal examination After the second trimester of pregnancy, the uterus increases beyond the corresponding pregnancy month. The abdomen can touch small limbs or more than two fetal poles in multiple places. Doppler and fetal heart stethoscope can be used after 3 months of pregnancy and 5 months after pregnancy. I heard two fetal hearts.

Pregnancy

The blood volume of pregnant women with twins is more than that of singletons. At the same time, it takes more protein, iron, folic acid, etc. for the two fetuses. In addition, the absorption and utilization ability of folic acid is reduced, and iron deficiency anemia and megaloblastic anemia often occur. In twin pregnancy, it is also easy to have hypertensive disorder complicating pregnancy, polyhydramnios, fetal malformation, placenta previa, placental abruption, postpartum hemorrhage, premature delivery, dystocia, intrauterine growth retardation, intrauterine stillbirth, abnormal fetal position. The fetal position of twin pregnancy is mostly vertical, and it is more common in head or head buttocks. Other fetal positions are less common. During twin pregnancy, due to uterine enlargement and high pressure, premature rupture of membranes and premature birth are prone to occur. The average weight of single-oval twins is lighter. In the twin pregnancy, the placenta area is large, sometimes extending to the lower part of the uterus and the internal cervix, forming a placenta previa leading to prenatal bleeding.

2. Childbirth

There are many abnormalities during twin birth, and the types are as follows:

(1) The prolongation factor of the labor process is large, the muscle fibers are excessively extended, and the primary uterine contraction is prone to occur, and the labor process is prolonged. After the first fetus is delivered, the second fetus may be prolonged due to uterine weakness.

(2) premature rupture of membranes and umbilical cord prolapse due to abnormal fetal position and combined with polyhydramnios, increased intrauterine pressure, prone to premature rupture of membranes and umbilical cord prolapse.

(3) Abnormal fetal position is generally small due to the fetus, often accompanied by abnormal fetal position. When the first fetus is delivered, the second fetus has a larger range of activity and is easy to turn into a shoulder.

(4) Placental abruption After the first fetus is delivered, the volume of the uterine cavity suddenly shrinks. As a result, the placenta attachment surface also shrinks, which becomes the pathological basis of placental abruption. In addition, twin pregnancy often combined with polyhydramnios. When the amniotic fluid is discharged, the volume of the uterine cavity is reduced, and placental abruption can also occur.

(5) Fetal head interlocking and fetal head collision are rare in clinical practice. If the first fetus is breech exposed and the second fetus is exposed first, the first fetal head has not yet been delivered during childbirth, and the head of the second fetus has fallen into the pelvic cavity, and the necks of the two fetal heads are interlocked together. Called the fetal head interlocking, causing dystocia. Both heads are exposed to the head at the same time, and the collision of each other causes obstructive dystocia. The above situation is likely to occur in small fetuses, excessive pelvis, second fetal amniocentesis or single amniotic sac twins.

(6) postpartum hemorrhage and puerperal infection due to excessive extension of uterine muscle fibers caused by uterine contraction, prolonged labor. In addition, the placenta has a large attachment surface and often causes bleeding after production. Due to the complications of twin pregnancy, often accompanied by anemia, poor resistance, there are two vaginal midwifery during childbirth, it is also easy to produce sputum infection.

Examination of twin pregnancy

Biochemical testing:

Since the twin placenta is larger than the singleton, the average level of human chorionic gonadotropin (HCG), human placental lactogen (HPL), alpha fetoprotein (AFP), estrogen, and alkaline phosphatase in biochemical tests and Urinary estriol and estradiol are indeed higher than singleton, but these methods have no diagnostic value, and only a significant increase in AFP will increase people's vigilance against deformity.

1.B-ultrasound

It is an important tool for diagnosing twins. It also has the function of identifying fetal growth and development, observing fetal malformation and whether there is excessive amniotic fluid or oligohydramnios.

(1) Diagnosis of twins in early pregnancy: Pregnancy with abdominal B-ultrasound is first seen in 6 weeks, general pregnancy can be found in 7-8 weeks, there are two embryo sacs in the uterus, but vaginal ultrasound can be more than abdominal ultrasound Early detection of twins, until 9 to 13 weeks of gestation, the two fetal sacs and their fetal movements are clearly identifiable, after 16 weeks of gestation, the double-diameter can be measured to observe the growth of the fetus, in case of double-horned uterus, due to a corner After internal pregnancy, the aponeurosis of the contralateral horn is affected by the ovary and placenta and the decidua is fully developed. The secretion of the gland is filled in the cavity and can cause saclike illusion and is misdiagnosed as twins (DAlton and Mercer, 1990).

In the early pregnancy, the number of twins diagnosed in B-ultrasound is higher, and the number of twins actually delivered in late pregnancy is higher, because in early pregnancy, one of the twins can die for various reasons, and one child disappears or dies in the palace. The incidence rate is from 20% (Jones et al., 1990) to 50% (DAlton Mercer, 1990). This phenomenon is called vanishing twin. The rate of multiple pregnancies in early pregnancy is 12 for all natural pregnant women. %, but only 14% of them survive to full term, the risk of abortion of single chorionic twins is significantly higher than that of double chorion twins.

(2) Diagnosis and monitoring of mid-late twin pregnancy: In the middle and late pregnancy, the correct rate of diagnosis of twins by B-ultrasound can reach 100%, except that there can be two fetal heads or trunks and visible fetal heart and different beats. Beyond the frequency, attention should be paid to the position of the twin placenta. On the one hand, it should be distinguished as a single or double-oval twin. On the other hand, attention should be paid to whether there is a placenta low or a placenta previa. In the late pregnancy, the two fetuses of the twins The growth rate is slower than that of a single fetus, and the two fetuses can sometimes be different. For example, the difference between the two fetuses is more obvious when the twin transfusion syndrome is accompanied. Therefore, the reference number of the two fetuses such as the biparietal diameter and the length of the femur should be used. Measurement of abdominal diameter, etc., to judge the developmental situation. In addition, attention should be paid to the monitoring of amniotic fluid. Joern et al. (2000) used Doppler ultrasound to monitor the umbilical blood flow velocity of the fetus in the late twin pregnancy to judge the prognosis of the fetus. Those with abnormal flow velocity, less than gestational age, premature delivery, cesarean section and perinatal mortality are significantly higher than normal, so it can also be used as one of the monitoring methods.

(3) Diagnosis of twin malformation: fetal malformation of twins is significantly higher than singleton, common malformations include hydrocephalus, no brain, meningocele, umbilical bulging and visceral eversion, double deformity and Unintentional deformity, etc., can be diagnosed by B-ultrasound.

2. X-ray diagnosis

X-ray examination was once an important method for diagnosing twins, but compared with B-mode ultrasound, its diagnosis must be used after bone formation, and maternal obesity, polyhydramnios and fetal movement affect the correctness of diagnosis, and radiation Certainly harmful, it is better to observe the structure of each part of the fetus through multiple cut surfaces, measure the diameter of the fetus, and can be used repeatedly, so it has almost been replaced by B-ultrasound.

Diagnosis and diagnosis of twin pregnancy

Since the extensive application of B-ultrasound technology in obstetrics, twin pregnancies can be found in early and mid-term pregnancy. Any family history of twins with HMG or clomiphene ovulation and pregnancy should pay attention to the possibility of twins. If the actual uterus size is larger than the uterus gestational month, or if the height of the uterus is greater than the height of the gestational month, there should be a suspected twin pregnancy. In the abdominal examination, such as sputum and excessive small limbs, or The three fetal poles should be suspected of having twins. If two fetal hearts with different rates can be heard at the same time, the diagnosis of twins may be made when the difference is 10/min (10bpm) or more.

Prenatal examination should consider twin pregnancy in the following circumstances

(1) The uterus is larger than the gestational week, and the amount of amniotic fluid is also high.

(2) In the third trimester, multiple small limbs, two fetal heads or three fetal poles are touched.

(3) The fetal head is small and disproportionate to the size of the uterus.

(4) Hearing two fetal hearts with different frequencies in different parts, counting 1 minute at the same time, the fetal heart rate differs by more than 10 times, or there is no sound zone between the two fetal heart sounds.

(5) The weight gain in the middle and late pregnancy is too fast, and it is not explained by edema and obesity.

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