一次妊娠有两个或两个以上的胎儿称为多胎妊娠,其中以双胎最多见。多胎妊娠的类型依据由1个卵子或多个卵子受精形成可分为:由一个受精卵分裂而成的双胎称为单卵双胎,由两个卵子分别受精形成的双胎称为双卵双胎。三胎最常来自三个卵子,称为三卵三胎,由一个卵子形成的为单卵三胎,也可来自双卵。四胎以上的多胎可由单卵或多卵形成,自然发生的四个以上的多胎很少见,但在应用促性腺激素或其他促排卵药物治疗不孕症时常可有多个卵泡成熟排卵,而多胎发生率增高。近代器官移植手术飞跃发展,由于单卵多胎的遗传基因相同,移植时不产生排斥反应, A pregnancy has two or more fetuses called multiple pregnancies, of which twins are the most common. The type of multiple pregnancy based on the fertilization by an egg or multiple eggs can be formed into: from a fertilized egg is divided into twin twins known as monozygotic twins, fertilized by two eggs, respectively, formed twins called double eggs Twins. The three most common babies come from three eggs, called three eggs and three babies, formed by an egg as a single egg or triplets, but also from double eggs. Multiple births more than four births can be formed by a single egg or multiple eggs, more than four naturally occurring multiple births are rare, but in the application of gonadotropin or other ovulation induction treatment of infertility often have multiple follicles mature ovulation, and The incidence of multiple births increased. Modern organ transplant surgery leaps and bounds, due to the same genetic multiple genes, transplantation does not produce rejection,