Will the antibiotic nitrofurantoin affect my birth control pill?

Yes: If you are taking Nitrofurantoin while using birth control pills, you should use a back-up method of birth control (ie. Condom). Despite the fact there is little evidence supporting a massive increase in pregnancies with antibiotic use, it is better to be safe than sorry. Use the back-up method during the run of your antibiotic and continue for one week afterwards.

Dr Fowler agreed

No interference: It's an outdated urban myth that antibiotics interfere with effectiveness of birth control pills. They do not, except occasionally with rifampin, an infrequently used antibiotic for certain infections like tuberculosis. And nitrofurantoin certainly has no effect. See https://www.drugs.com/article/antibiotics-and-birth-control.html