Many pregnant women wish they could have two babies and save time and trouble by having two babies at once. Is this really the case? From a medical science point of view I would like to tell you that you really should not try to have a twin pregnancy so easily. Why is that? This is because twin pregnancies are associated with increased risks for both mother and baby during pregnancy compared to singleton pregnancies. One of the most serious complications is twin pregnancy transfusion syndrome. Twin pregnancies can be divided into two types: one is due to two eggs being expelled and fertilized separately, which is called dizygotic twins and accounts for about 70% of twin pregnancies; the other is due to a single fertilized egg dividing to form two genetically identical fetuses, which accounts for about 30% of twins, both of the same sex, and is called monozygotic twins. Twin-twin transfusion syndrome (TTTS) may occur in 2/3 of monozygotic twins. In addition to dizygotic transfusion, monozygotic twins may also develop twin reverse arterial perfusion syndrome (TRAPS), twin anemia-polycythemia sequence (TAPS), selective fetal growth restriction (SFGR), and intrauterine death of one of the twins. The pathogenesis of TTTS, which usually develops between 16 and 26 weeks of midtrimester, is that the twin fetuses share a placenta in which blood vessels traffic with each other, resulting in a constant flow of blood from one fetus to the other. Eventually, one fetus is too large and one is too small; one has too much amniotic fluid and one has too little; one is anemic and one has too much blood leading to heart failure, so both fetuses have a poor prognosis. Clinically, TTTS is mainly diagnosed by ultrasound. It is recommended that ultrasound should always be done in early pregnancy to determine chorionicity and to assess the possibility of TTTS in twin pregnancies. If the doctor advises the possibility of TTTS, it is advisable to perform ultrasound every 2-3 weeks during pregnancy for early detection of TTTS and early treatment. Without treatment, the mortality rate for both fetuses is about 90%. Nowadays, for more severe TTTS, fetoscopic intra-placental anastomotic vascular laser electrocoagulation can be performed to coagulate the blood vessels causing two fetuses to transfuse with each other, and this procedure can significantly improve the prognosis of children with TTTS, with a survival rate of 85% for a single fetus and up to 60% for both fetuses. Amniotic fluid reduction can also be used in milder cases of TTTS to alleviate the condition and achieve longer gestational weeks. However, if it is found too late and one fetus is already severely stunted, then only reduction can be done. We hope that all pregnant women with twin pregnancies will have a safe and successful pregnancy and have two healthy babies!