The birth of a baby is a twin birth, resulting from the simultaneous fertilization of two sperm and two eggs, which then form two separate fertilized eggs. The blood group of the twins is determined by the blood group genes contained in the two sperm and two eggs, which may be the same or different. Due to the different sexes of twins, the karyotypes and genes of the chromosomes of the two fetuses are also different. Generally, the blood types of the two fetuses, commonly known as ABO blood group and Rh blood group, are inherited as dominant blood group genes, which may be the same or different, and can be tested for blood group after birth. Twin pregnancies have more complications during pregnancy than single pregnancies, and chorionic villus testing is usually needed early in the pregnancy. Chorionicity in twins is a double chorionic villus and double amniotic sac twin pregnancy, which requires routine prenatal screening in the second trimester, as well as prenatal diagnosis if necessary. During the period of pregnancy, pregnant women should maintain a happy mood, pay attention to rest and warmth, eat more nutritious food, and the need to do regular pregnancy checkups to avoid accidents.