Group B streptococcus
Although it only affects approximately one in every 2,000 babies born in the U.S., the bacterial infection known as group B streptococcus (GBS) can have serious consequences, so doctors (and the CDC) recommend that all pregnant women be tested -- usually during the 35th to 37th week of their term [source: American Pregnancy Association]. The test is conducted through a vaginal and anal swab that checks for the bacteria, which is actually present in approximately 25 percent of all healthy women [source: American Pregnancy Association].
If the test comes back positive, there is a one in 200 chance that a baby will contract the disease during birth, which can lead to serious conditions like sepsis, pneumonia and meningitis. However, if antibiotics are administered intravenously during delivery, that risk drops to one in 4000 (source: American Pregnancy Association). Antiobiotics are particularly recommended for a woman whose water breaks more than 18 hours before delivery, who has a fever during labor, who goes into labor early, or who has a history of giving birth to a child who contracted the disease.