With the increase in the age of pregnant women and the promotion of assisted reproductive technology, the incidence of twin births has been increasing year by year, and the latest information shows that the incidence of twin births is 1-3%. Most families are filled with joy and pride when they learn that the baby is a twin in the womb. However, as maternal-fetal medicine specialists, we have to remind mothers that twin pregnancies are high-risk pregnancies, with a higher maternal morbidity rate than singleton pregnancies, and a significantly higher fetal and neonatal morbidity rate.
What are the risks for pregnant women with twin pregnancies?
Combined hypertensive disorders of pregnancy: The risk of complications of hypertension during pregnancy is 3-5 times higher in women with twin pregnancies than in singleton pregnancies, and this risk increases with gestational age. If complicated by severe hypertension, serious complications such as convulsions, cerebral hemorrhage, heart failure, and placental abruption may occur.
Postpartum hemorrhage: twin pregnancies are prone to hemorrhage and even life-threatening in severe cases due to excessive uterine distension and weak uterine contractions during and after delivery.
Difficult delivery: In twin pregnancies, after the first fetus is delivered, the other fetus is prone to transverse delivery, which can cause obstructed labor, uterine rupture, placental abruption, or stillbirth of the second fetus.
What are the risks to the fetus and newborn in twin pregnancies?
1, preterm delivery: twin pregnancy is prone to premature rupture of membranes and preterm delivery due to high uterine tension, with a preterm delivery rate of nearly 50%. Premature birth, especially before 34 weeks of gestation, may result in pulmonary hyaline membrane lesions, hypoxic-ischemic encephalopathy, DIC, and even perinatal death.
2. Intrauterine growth retardation: After 28 weeks of gestation in twin pregnancies, the development of each fetus gradually lags behind that of the singleton fetus at the corresponding gestational week. The limited capacity of the uterus, especially for short, obese and thin pregnant women, the limited space and nutrition supply will inevitably cause both fetuses to be stunted (called non-selective fetal growth retardation) or one of them to be far behind the other (called selective fetal growth retardation). The chance of hypoxia and neonatal cerebral palsy is significantly higher in fetuses with developmental delay.
3. Spontaneous abortion: The incidence of spontaneous abortion in twin pregnancies is twice as high as in singleton pregnancies. Due to the improvement of ultrasound diagnosis technology, more and more cases of early miscarriage and death of one of the twin pregnancies can be diagnosed in time. Therefore, it is recommended that every woman of childbearing age should have an ultrasound examination to determine the number of fetuses as soon as she is informed that she has conceived.
4. Complications specific to monochorionic twins: Whether conceived naturally or through assisted reproductive technology, there is a chance of monochorionic twins. Although monochorionic twins account for only 30% of all twins, they can have serious fetal complications, such as twin transfusion syndrome, selective fetal growth retardation, twin reverse perfusion syndrome (also known as heartless twins), twin anemia-polycythemia syndrome, twin fetal anomalies, and twin fetal death. If left unattended, it can be complicated by simultaneous death of both fetuses, neonatal cerebral palsy, neonatal heart failure, and neonatal death.
What are the types of twin births? What are the most dangerous types of twins?
Monozygotic twins and dizygotic twins are classified according to their ovality. As the name suggests, monozygotic twins are two fetuses that develop from the same fertilized egg, while dizygotic twins are two fetuses that develop from two fertilized eggs. All dizygotic twins are dichorionic dichorionic twins (DCDA). Depending on the nature of the chorionic villi, monozygotic twins are subdivided into dichorionic chorionic twins (DCDA) and monochorionic chorionic twins (MCDA and MCMA). The timing of the fertilized egg division determines the chorionic villous nature of monozygotic twins. Those in which the fertilized egg divides within 72 hours of conception form a double chorionic villous double amniotic sac twin (DCDA), with each fetus having separate chorionic and amniotic cavities, with relatively few fetal complications and a good fetal prognosis. A single chorionic villous double amniotic sac twin (MCDA) is formed when the fertilized egg divides 4-8 days after conception. Those that divide 8-13 days after fertilization form a monochorionic monochorionic villous membrane twin (MCMA). In both MCDA and MCMA twins, both fetuses share a common chorionic cavity, the placenta fuses with each other, and a large number of vascular cross-anastomoses are formed on the placenta; this type of twin accounts for only 30% of all twins, but the fetal mortality rate is as high as 50%. It is therefore important to diagnose the nature of the fetal chorionic villi early and to screen for complications of monochorionic twins.
How is the nature of the chorionic villi diagnosed in twin fetuses?
The diagnosis of chorionic villus nature needs to be determined based on the pathological examination of the placenta after delivery. If the two placentas are completely separated and the septum between the fetuses is composed of 4 membranes, the twin is DCDA. If the placentas are fused into one and the interfetal septum is composed of 2 membranes, the fetus is an MCDA twin. If there is no septum between the fetuses, the fetus is an MCMA twin.
The nature of the chorionic villi can also be predicted by ultrasonography in early pregnancy. For example, at 6-10 weeks of gestation, the number of gestational sacs can be determined by the number of gestational sacs. If two separate gestational sacs are visible on ultrasound, the pregnancy is a double chorionic twin; if only one gestational sac with two germ buds is visible on ultrasound, the pregnancy is a single chorionic twin. From 11 to 16 weeks of gestation, the thickness of the interstitial septum and the angle between it and the placenta are observed under ultrasound. If the septum is thick and the angle is λ-shaped, then it is a double chorionic twin; if the septum is thin and the angle is T-shaped, then it is a single chorionic twin. It should be emphasized that after 20 weeks of gestation, the thickness of the interstitial septum and the angle between it and the placenta can no longer accurately predict the nature of the chorionic villi. Therefore, once a twin pregnancy is known, the nature of the chorionic villus should be determined promptly in early pregnancy to guide subsequent monitoring and to gain time for prevention of complications.
What is twin-fetus transfusion syndrome? What are the treatment options?
Twin-to-twin transfusion syndrome (TTTS) is the most common complication in monochorionic twins. The incidence is 30% of monochorionic twins. Its poor perinatal prognosis and the high risk of maternal complications make it one of the most concerned conditions in maternal-fetal medicine. Due to the large amount of vascular traffic between the placentas of monochorionic twins, the two fetuses are in direct blood communication. One fetus is a blood donor fetus with developmental delay, anemia, oliguria, low amniotic fluid, and hypotension; the other fetus is a blood recipient fetus with polycythemia, polyuria, excess amniotic fluid, cardiomegaly, hypertension, and edema. The donor fetus may die in utero due to fetal distress. The recipient fetus may also die due to heart failure. The diagnosis is made mainly by ultrasound. Differences in fetal head-rump diameter and posterior cervical cortex thickness can be detected as early as 14 weeks of gestation. Differences in amniotic fluid volume between the two fetuses, bladder volume differences, changes in the Doppler spectrum of blood flow, and edema gradually appear after 18 weeks of gestation.
The current treatment for TTTS is mainly sequential amniotic fluid reduction, selective fetal reduction, and fetoscopic placental anastomosis with vascular laser coagulation, which can be selected according to the onset gestational week, severity of the disease, fetal complications, and parents’ expectations for the fetus.
After years of accumulation and close communication with international advanced fetal centers, we have developed a procedure for monitoring twin pregnancies:.
1., Ultrasonography is performed at 8~12 weeks of gestation to clarify the chorionic nature of the twin fetuses, and the risks of twin fetuses are explained to the pregnant women according to the results of chorionicity, and the principle of informed consent is fully fulfilled.
The NT value of each fetus is determined by ultrasound at 11-13+6 weeks of gestation, and those with abnormal NT values are referred to the “twin pregnancy specialist” (every Monday morning).
3. For single chorionic twins, ultrasound examination will be performed every 2 weeks from 16 weeks of gestation to evaluate the fetal status. If the ultrasound result is abnormal, refer to “twin pregnancy specialist”.
4. Pay attention to monitoring blood pressure, weight and urine protein to detect and diagnose hypertensive disease in pregnancy in time and give appropriate treatment.
5.After 28 weeks of gestation, appropriate rest can be given to prevent preterm delivery.
6.In the absence of special circumstances, hospitalization at 36~37 weeks of gestation, discussion with pregnant women and their families on fetal orientation, fetal size, and the presence of complications, decision on the mode of delivery, and planned delivery at a later date.