A study from the Centers For Disease Control and Prevention finds a higher than expected rate of false-negative- test results for a bacteria pregnant women might carry.
The bacteria -- called Group B Strep -- are often harmless in adults, but can be dangerous to babies.
Group B strep is relatively common, and found in the intestines or lower genital tract in adults.
If a pregnant woman is infected, she likely won't have any symptoms, but may spread it to her baby during delivery.
Infected newborns can suffer a number of severe problems -- including blood infections, pneumonia, blindness or death.
Although infections in newborns are rare, doctors began screening pregnant women for the bacteria in 2002.
If the test results are positive, the woman receives antibiotics during delivery to protect the baby.
Researchers at the C-D-C looked at data on Group B infections from 10 states, and found 60-percent of infected babies were born to mothers whose Group B strep test results were negative.
Now researchers will try to figure out why this is happening. It may be that mothers acquire the bacteria - after- being screened. Overall, though, experts say the screening has been successful, and that the antibiotics seem to work very well.