一次妊娠同时有两个或两个以上的胎儿时,称为多胎妊娠,其中以双胎妊娠为常见。多胎妊娠的发生率,按Hellin氏公式计算为1:89~(n-1)(n代表一次妊娠中的胎儿数),亦即每89次妊娠中有一次双胎。一次分娩生下两个新生儿,称为孪生,俗称为“双胞胎”。两个新生儿由同一个受精卵分裂而产生者,称为单卵孪生或同卵孪生;来源于两个受精卵者,称为双卵孪生或异卵孪生。单卵双胎约占双胎中的1/3。 A pregnancy with two or more fetuses at the same time, called multiple pregnancy, which is common twin pregnancy. The incidence of multiple pregnancies, calculated according to Hellin’s formula, is 1: 89 to (n-1) (n represents the number of fetuses in a single pregnancy), ie, one in every 89 pregnancies. One childbirth gave birth to two newborns, called twins, commonly known as “twins.” Two newborns produced by the same fertilized egg division, known as single egg twins or identical twins; derived from two fertilized eggs, known as double egg or twins. Twin eggs about twins in the 1/3.