Two offspring resulting from one pregnancy. Monozygotic, or identical, twins develop when a single fertilized egg divides at an early stage of development. Incomplete division of the egg results in conjoined twins (see Siamese twins). Monozygotic twins share the same placenta. Dizygotic twins develop when 2 eggs are fertilized at the same time. They each have a placenta and may be of different sexes. Twins occur in about 1 in 80 pregnancies. (See also pregnancy, multiple.)
Twins |
|
|