Objective. To evaluate the role a daily intake of 100 mg of ascorbic acid plays in urinary infection prophylaxis during pregnancy. Methods and materials. A single-blind clinical trial was carried out on pregnant women randomly assigned to the following treatment groups — Group A: oral treatment with ferrous sulphate (200 mg per day), folic acid (5 mg per day) and ascorbic acid (100 mg per day) for 3 months, and Group B: oral treatment with ferrous sulphate (200 mg per day) and folic acid (5 mg per day) for 3 months. All patients were clinically evaluated, and a urine culture was carried out each month for a period of 3 months. The χ2 and odds ratio were used to compare effects with and without ascorbic acid, and statistical significance was considered at p<0.05. Results. Global frequency of urinary infections was 25%. The presence of urinary infections in Group A (12.7%) was significantly lower than in Group B (29.1%), (p = 0.03, OR = 0.35, CI 95% = 0.13–0.91). Conclusions. Daily intake of 100 mg of ascorbic acid played an important role in the reduction of urinary infections, improving the health level of the gestating women. We recommend additional vitamin C intake for pregnant women in populations which have a high incidence of bacteriuria and urinary infections.