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.
About 60 percent of all twins are born prematurely. This probably has something to do with the fact that the uterus (or in this case, the double uteruses) can only expand so much. In some women with this condition, the two uteruses cannot expand as much as a normal, single uterus would.