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.
Fraternal twins and identical twins differ in how the set of twins arise. Fraternal twins occur when a woman releases two eggs during ovulation instead of just one (which is what is normally released). Each of these eggs can then be fertilized by a different sperm cell from the father.