I am 25 weeks pregnant and my urine culture report shows: growth of three types of gram negative bacilli. what does it mean?

Maybe nothing: Gram negative bacilli bacteria are often the cause of urinary tract infections. However, it depends on how the sample was collected. Urinating into a cup can often cause bacteria from surrounding tissue/vulva/vagina to wash into the cup making it appear like you have a UTI. Pregnancy often causes a heavier vaginal discharge, so contamination of a sample is more likely. Review test with dr.

Possible infection: Most people with bladder (urinary tract) infections have only one bacteria causing the infection. Having three different bacteria causing an infection is possible but rare. More often, there are several bacteria picked up off your skin when you urinated, and these are the bacteria that grew in the lab culture. See your doctor for a repeat culture; if you have symptoms, continue treatment.