Most antibiotics don't affect contraception. It is now thought that the only types of antibiotic that interact with hormonal contraception, and make it less effective are rifampicin-like antibiotics.

These can be used to treat or prevent diseases, including tuberculosis and meningitis. They include:
rifampicin
rifabutin

These types of antibiotics can increase the enzymes in your body. This is known as being "enzyme-inducing", and can affect hormonal contraception.
If you are taking enzyme-inducing antibiotics while using hormonal contraception, to avoid getting pregnant you'll need to use additional contraception, such as condoms.

Macrobid is not an "enzyme inducer" so in theory should not reduce the birth control pills effectiveness.

However, until more is known, most doctors recommend while taking Macrobid an additional method of contraception is required.

https://www.drugs.com/interactions-check.php?drug_list=1724-1082,1045-9722