I was just reading about this subject, actually. This is from The Encyclopedia of Health - Psychological Disorders and their Treatment - Schizophrenia (ed. Solomon H. Snyder)
...Equally baffling are the cases of women who suffer schizophrenialike symptoms after childbirth. Although it is not uncommon for a new mother to suffer some depression following delivery of her baby, about 1 woman in 1000 suddenly develops sign of schizophrenia 3 to 7 days after giving birth.
(Gives some examples)
What triggers these symptoms is unknown. Psychological theories suggesting that delusions and hallucinations stem from the mother's ambivalent feelings about her child were once widely accepted. Today, biology is a prime suspect. A leading theory suggests that enormous changes in a woman's hormones that occur during and after birth are somehow responsible. Again, such symptoms do not represent actual schizophrenia. Most women recover with no future problems. Some do end up becoming schizophrenic, but experts believe they would have developed the disease even if they had never given birth.
These are from pages 38-39.
There is a great amount of evidence to suggest that schizophrenia is genetic so the chances of your wife having it are even greater. Furthermore, there is a fair chance that your child will have it as well.
If I were you, I'd adopt.