Fetal reduction is a procedure to reduce the number of fetuses in patients with twin and multiple pregnancies. With the use of ultrasound, the majority of multifetal pregnancies can now be diagnosed in early pregnancy, especially in patients assisted by assisted reproductive technology, and most pregnant women with high sequence of multifetal pregnancies (three or more) have been counseled and undergone reduction of multifetal pregnancy (specifically at 5-12 weeks, by transvaginal sac aspiration or transabdominal intracardiac potassium chloride injection) in early pregnancy. This article is specifically aimed at pregnant women who require reduction of the number of fetuses in the second trimester (13 weeks or more), especially for some fetal anomalies that appear only in the second trimester. Before visiting the Fetal Medicine Center, you can read the following to understand the pros and cons of the risks associated with the reduction procedure in midtrimester. I. Indications for midtrimester elective fetal reduction: 1. Midtrimester elective fetal reduction is mainly used for the treatment of complicated twin complications, including severe malformation of one of the twins, type II and III selective fetal growth restriction (sIUGR), severe twin-to-twin transfusion syndrome (TTTS), twin reverse arterial perfusion (TRAP), and umbilical cord entanglement in single amniotic sac twins (MCMA). Except for one of the twin malformations that can occur in twin chorionic twins, the other conditions are only seen in single chorionic twins. Here again, patients are reminded that the determination of chorionicity in early pregnancy (8-12 weeks) is crucial and determines the choice of treatment after various complications arise in midtrimester. See my top article for more details. If there are no such complications, but only due to maternal physical factors or the patient’s wish to reduce the number of fetuses, the patient needs to be fully aware of the pros and cons of fetal reduction surgery, understand the alternative treatment options available, and decide carefully whether to undergo fetal reduction. This includes pregnant women of advanced age, those with a history of cesarean delivery, those with heart or liver or kidney disease, and families with healthy children who do not wish to raise more than one child. After all, each procedure is a double-edged sword, and the benefits come with corresponding risks. Patients and their families should give full consideration before making a decision. 3. The role of fetal reduction in patients with three pregnancies is still controversial. Some experts believe that reduction is not necessary for third trimester pregnancies and that pregnancy outcomes can be improved by strengthening pregnancy care and preventing preterm delivery. It has also been suggested that the benefits of reduction are mainly an increase in pregnancy success rate from about 75% to 85% and an increase in gestational weeks of delivery from an average of 33 weeks to 36-37 weeks, but the risks are the early miscarriage rate after reduction, which is related to the number of fetuses reduced. 3-1 (i.e., retained twin) patients have a lower early miscarriage rate after reduction but a higher preterm birth rate, while 3-2 (retained singleton) have a higher early miscarriage rate after reduction. The early miscarriage rate is higher, but once the risk period of about 2 weeks is passed, the probability of preterm delivery is reduced. In conclusion, each has its own advantages and disadvantages, and a comprehensive decision is needed based on the nature of the chorionic villi, fetal position, and ease of operation of the three fetuses. The procedure for elective reduction of fetus in mid-trimester: 1. Double chorionic twins: Both in early and mid-trimester, reduction can be performed by injection of potassium chloride, which has been confirmed to be safe and effective by a large sample study. In midtrimester, due to the high fetal movement and variable fetal position, it is sometimes difficult to puncture the fetal heart or chest cavity, and the increase in the number of punctures may also cause discomfort to the patient. Therefore, if the traditional intracardiac or intrathoracic injection of potassium chloride is difficult to perform, intracranial injection of potassium chloride into the fetal head may also be chosen for fetal reduction. 2. Single chorionic villus and double amniotic sac twin fetuses: Because of the presence of traffic vessels between the two fetuses, potassium chloride injection is not suitable for fetal reduction, and other methods can only be used for fetal reduction, such as fetoscopic cord ligation, or techniques to occlude the umbilical cord by various high-energy methods, including bipolar electrocoagulation, laser coagulation, radiofrequency ablation, and the recently reported use of microwave ablation and high-intensity focused ultrasound (HIFU) techniques for fetal reduction. All of these procedures are based on the same principle of reducing the fetus by blocking the abnormal umbilical blood flow through mechanical or energetic means without affecting the normal fetal blood supply. The overall pregnancy outcome of the above methods is not very different, and the choice of surgical method depends more on the experience and habits of the operator. The risk of intrauterine fetal death in MCMA is higher due to the combination of umbilical cord tangles and knots. If one of the MCMA twins is malformed, elective reduction can be performed. If there is only umbilical cord entanglement without fetal malformation, whether to perform reduction needs to be decided together after full communication with the patient and family. If elective reduction is performed for MCMA, a fetoscopic cord ligation + cutting + unwinding is required. The surgical outcome is definitive but difficult. As of 2014, the number of surgical cases of intrauterine fetal treatment in MCMA is only about a hundred cases worldwide, and the overall neonatal survival rate is about 75%. 4. Twin reverse arterial perfusion sequence signs: Not all TRAPs need to be treated by decompression surgery. If the growth of a heartless fetus is faster than that of the donor fetus, it can lead to overload of the heart of the donor fetus and heart failure or even intrauterine death; if the heart of the donor fetus is enlarged, tricuspid regurgitation, edema and other manifestations, it indicates a higher risk of heart failure in the donor fetus and intervention should be given. The operation of fetal reduction in such patients is often more difficult, due to the obvious edema of the heartless fetal mass, resulting in increased surgical difficulty, relatively longer operation time, higher percentage of premature rupture of membranes occurring after the operation, and decreased success rate of the operation. The microwave ablation technique proposed in recent years is not affected by the amount of fluid in the tissues, so it may be more suitable for the reduction of a heartless fetal mass with severe edema. The timing of fetal reduction surgery and the choice of fetal orientation Generally it is necessary to consider fetal reduction surgery only after the fetal abnormality is detected by ultrasound, in this case we cannot choose the fetal size and position, and only the one with definite abnormality may be reduced. However, if no definite fetal abnormality is found, we need to consider the timing of the reduction procedure and the choice of fetal orientation if maternal factors require it. At early gestational weeks, the surviving fetus may develop abnormalities later in life that cannot be observed at earlier gestational weeks. However, at larger gestational weeks and higher fetal weight, the dead fetus produces more necrotic material, which has potential effects on both the surviving fetus and the mother. In our clinical experience, the clinical prognosis is worse if the stillborn fetus is located below the uterine cavity than if it is located above the uterine cavity, with a smaller gestational week of delivery and a significantly lower live birth rate, possibly related to the fact that the stillborn fetus is more likely to cause premature rupture of the membranes when it is located below. Therefore, in elective reduction, if the abnormal fetus is located below the uterine cavity, the patient should be informed of the higher risk of early postoperative premature rupture of membranes and preterm delivery in particular, and a careful decision is needed.