multiple birth

The production of a clone (an exact replica) happens naturally when a zygote undergoes division. This is the process that brings about multiple births such as identical twins and triplets. Zygote division can be induced in vitro with the resulting embryos then implanted into surrogate mothers. The offspring are all clones of each other but not of their parents.

In humans, the production of more than two babies from one pregnancy. Multiple births can be caused by more than two eggs being produced and fertilized (often as the result of hormone therapy to assist pregnancy), or by a single fertilized egg dividing more than once before implantation. See also twin.

In November 1997, after having undergone fertility treatment, an American woman, Bobbi McCaughey, gave birth to then the world's only known surviving septuplets (four boys and three girls). A survey published in August 2001 found that between 1980 and 1997 the twin birth rate in the USA increased by 42% and the rate of larger multiple births increased by 370%. These increases were attributed to the increased effectiveness of fertility treatment.