Hello Thanks for your query. If your wife is having JUST plain yellow discharge, there is no emergency. During pregnancy, some amount of discharge is perfectly normal. If the discharge is accompanied by pain, cramps, feeling of pressure or dragging in the lower abdomen, or tightening of the uterus, then you need to be worried about the possibility of preterm labour. Also, if there is bad odour, vaginal itching , pain etc, then the discharge could indicate a pelvic infection, which can again lead to preterm labour. In absence of any other complaints, you can wait till your next visit to the obstetrician when you could have a check up for the discharge. take care