loose motions can be because of any infection which might have got transmitted by unknowingly eating any contaminated food or touching contaminated utensils etc,
anyhow during pregnancy
it should be treated early to prevent dehydration
and uterine contraction s causing preterm labor
so you better take your wife to gynecologist let her examine for well being of the baby, then with her advice she can take oral rehydration fluids and antibiotics.