twin [AS, twinn, double] , either of two offspring born of the same pregnancy and developed from either a single ovum or from two ova that were released from the ovary simultaneously and fertilized at the same time. The incidence of twin births is approximately 1 in 80 pregnancies. Kinds include conjoined twins, dizygotic twins, interlocked twins, monozygotic twins, Siamese twins, unequal twins. See also Hellin’s law.
