Just recently I tried to update my knowledge on this very commonly asked question.
I found that FDA approves it as a safe food ingredient.There is no clear association between short attention span in babies and Ajinomoto.The research on monkeys didn't show passage of MSG or ajinomoto through the placenta.Only animals who have been affected are, the rats, that too in whom the MSG or Ajinomoto was injected.
So FDA approves it as GRAS substance (Generally recognized as safe).
you can follow the link for any further queries.
So ,perhaps you can occasionally indulge in 'Chinese' at your favourite restaurant after all while you are pregnant.