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.
Meaning, having twins in your family will make no difference in the possibility of conceiving identical twins. Identical twins seem to occur randomly throughout the population without rhyme or reason. Fraternal twins (dizygotic) occur when two separate eggs are fertilized by two separate sperm. Two separate babies with no more in common than siblings born at different times are formed. Fraternal twins can be the same sex and/or blood type.