Among cultures that believe in reincarnation, congenital abnormalities are commonly viewed as clues to the child's past life. Often they are tied in with the death of the supposed previous personality. Ian Stevenson's Reincarnation and Biology contains ten examples of children with birthmarks or birth defects corresponding to the place their alleged previous personality was shot or otherwise fatally wounded.
The birthmark business has a historical corollary of sorts in the theory of maternal impressions. A surprising majority of sixteenth and seventeenth-century physicians believed that a child's birthmarks or abnormalities are caused by the mother having undergone a memorable fright during pregnancy. A baby is born with a missing arm; the mother recalls being set upon by a one-armed beggar. A child's "fish scales" - a skin condition now known as ichthyosis - are blamed on the mother's fear of sea serpents.
By some accounts, mom didn't need to be frightened but merely focused a little too long in one place. In a famous case detailed by Jan Bondeson in A Cabinet of Medical Curiosities, a thirteenth-century Roman noblewoman gives birth to a boy with fur and claws; the authorities lay blame on an oil painting of a bear on her bedroom wall. The event prompted Pope Martin IV, clearly a tad hysterical, to have all pictures and statues of bears destroyed. Crafty moms tried to work the phenomenon to their favor. In the early 1800s, Bondeson writes, it was common for pregnant noblewomen to be wheeled into the Louvre to spend an hour or so gazing at a portrait of some handsome earl of archduke of yore, in hopes of influencing their unborn progeny.
Reports of maternal impressions peppered medical texts from Pliny and Hippocrates clear through to the 1903 edition of the American Textbook of Obstetrics, which cites maternal impression as the likely cause of John "Elephant Man" Merrick's deformities - as well as those of the lesser-known traveling spectacle, the Turtle Man.
In many of the birthmark cases in Reincarnation and Biology, Stevenson points out that the mother saw the corpse of the slain man whose soul eventually turns up in her unborn child. Stevenson doesn't believe all birthmarks are caused by maternal impression, but he is open-minded to the possibility that some are.
Adherents of maternal impression theory hold that the skin is uniquely vulnerable to emotional imprinting. Stevenson describes a half dozen dermatological conditions thought to be open to psychological influence. These range from the relatively mainstream (emotionally induced wheals and blisters) to the distant borderlands of scientific acceptability (stigmata, wart-charming, hypnotically-induced breast enlargement). I suppose that if you believe that hypnotic suggestion can expand a bosom, it's not a big leap to suppose that a profound fright might affect the skin of a developing fetus.
I love stories about reincarnation - children remembering people, things and places that they never could have known about except from a paste life... spooky but cool! These stories about a mother's fright causing a baby's birth defect seem odd to us, but aren't so different from many pregnancy superstitions that we may hear coming from our own cultures or others.