Diprosopus, also known as craniofacial duplication, is a rare congenital disorder. Babies both with this condition are generally considered a type of conjoined twin. These babies often have two sets of facial features. Some may have only a few duplicate facial features. For instance, two noses or two pairs of eyes may appear on the face, while other facial features appear as normal. In the most extreme cases of diprosopus, two complete faces can be found on a single head. The rest of the body generally appears normal.
Conjoined twins are rare, occurring in only about 10% of twins born alive. Conjoining of twins is believed to occur between the 13th and 25th days of pregnancy. Conjoining of twins probably occurs when two sperm fertilize the same egg, and the embryo fails to properly split into two separate fetuses. Diprosopus is considered the most rare form of conjoined twin, with only about 35 recorded cases occurring in the whole world since the condition was first documented in 1884.
Most fetuses stricken with this severe developmental abnormality are stillborn. Many babies born alive with diprosopus don't live long after birth. In 2008, a baby girl named Lali Singh was born in the Indian village of Saini. Lali was born with complete craniofacial duplication, meaning that she possessed two complete faces on a single head. Though Lali was believed to be in otherwise good health at the time of her birth, doctors believe her condition caused serious complications that ultimately led to her death at six weeks of age.
When this condition is discovered during pre-natal ultrasounds, abortion is usually recommended. These fetuses often suffer serious abnormalities in addition to craniofacial duplication. Spinal and brain abnormalities have been spotted on fetuses with diprosopus. These babies often possess two brains as well as two faces, but these brains are usually improperly formed. Some fetuses with diprosopus have been found to be lacking in proper cerebral development, and suffering from hydroencephaly.
These babies generally have a poor chance of surviving in utero until birth, and those that do usually don't survive long after. Babies with craniofacial duplication have been known to survive after birth, if only one brain is present. These fetuses usually develop abnormally large heads, which can make natural vaginal birth dangerous for the mother.