Hi and welcome to HCM
Pregnant women undergo a significant hormone change in a relatively short time period. During all 
pregnancy phases  early pregnancy to childbirth, the changes brought forth affect 
vaginal discharge, which can generate an odor.
Its true that vagina smells a peculiar odor, during pregnancy, but if its too fishy smell or is rather powerful that there might be trouble. 
Watch out for these symptoms
    Discharge that’s similar in texture to cottage cheese
    Pain/discomfort during sexual activity or urinating
    Yellow/green tint discharge
    Discharge that smells like yeast
    Bloody discharge (and you’re not having your period)
    Itchiness/inflammation of vagina.
If any of the above with fishy smell discharge is there, then better to contact your obstetrician for diagnosis of possible vaginal infection
Regards
Dr Santosh