Rhonda J. Pomerantz, MD is a practicing Dermatologist (Skin Specialist) in New York, NY. Dr. Pomerantz graduated from New York University School of Medicine in 1989 and has been in practice for 28 years. She completed a residency at Suny Health Science Center. Dr. Pomerantz also specializes in Internal Medicine.
Identical twins form when one egg has been fertilised by one sperm and the zygote splits into two. This happens at the very earliest stage of development, when the zygote is no more than a cluster of a few cells.
Things to remember. 1  Twins account for over 90 per cent of multiple births. 2  To form identical or monozygotic twins, one fertilised egg (ovum) splits and develops into two babies with exactly the same genetic information. 3  To form fraternal or dizygotic twins, two eggs (ova) are fertilised by two sperm and produce two genetically unique children.