If your provider is an OB, you will likely be tested for Group B Strep (GBS) between 35 and 37 weeks by swabbing the vagina and rectum.  GBS is caused by naturally occurring bacteria in the intestinal tract.  The presence of GBS during routine screening does not mean that the mother is currently or will become ill; it simply means that she is a carrier.  GBS can bring with it potential risks to a baby including pneumonia, meningitis, cardiovascular and pulmonary instability, gastrointestinal and kidney problems.  It is important to note that while these risks are serious considerations, they are not a guaranteed risk to the baby just because the mother is GBS positive.  

If a mother tests positive for GBS and she is using an OB as her provider, she will likely be pushed to allow IV antibiotic medication (typically penicillin), during labor to reduce the risks to the baby.  There are many natural remedies that pregnant mothers can take to avoid administration of antibiotics during labor.

For more information:

http://www.americanpregnancy.org/pregnancycomplications/groupbstrepinfection.html