Group B Strep Testing In Pregnancy: What Parents Need To Know
If you’re in your third trimester, chances are your provider has mentioned Group B Streptococcus (GBS) testing. For many parents, this conversation raises more questions than answers:
What is GBS, and how common is it?
What are the actual risks for my baby?
Do I really need antibiotics in labor if I test positive?
Let’s unpack the evidence step by step so you and your partner can feel informed and confident.
What Is Group B Strep?
Group B strep is a naturally occurring bacteria that lives on the skin and in the intestines. About 1 in 4 pregnant women (25%) carry it in the vagina or rectum at any given time. Most people never know they have it—because outside of pregnancy, it rarely causes problems.
In pregnancy, however, GBS can sometimes be passed to the baby during birth.
What Are the Risks for Newborns?
Here’s how the numbers break down:
Colonization in mothers: About 1 in 4 moms (25%) carry GBS.
Transmission to babies: If a mother has GBS, about 1 in 2 babies (50%) will also carry the bacteria after birth.
Developing disease (without antibiotics): Of those colonized babies, about 1–2 in 100 develop serious infection (early-onset GBS disease).
🔹 Put together:
Out of all babies born to GBS+ mothers, about 1 in 200–400 will get sick if antibiotics aren’t used.
Across the whole population (all births), that works out to 1–2 cases per 1,000 live births.
With Antibiotics in Labor
If the mother receives IV antibiotics during labor:
The risk of a newborn developing early-onset GBS disease drops to about 1 in 5,000 babies.
What Can Happen if a Baby Gets GBS Disease?
Most babies who develop GBS disease recover fully. But in rare cases, it can cause:
Sepsis (blood infection)
Pneumonia
Meningitis
Mortality rates today are low—around 2% for full-term babies—but higher for preterm infants.
What About Antibiotics in Labor?
If you test positive for GBS, the standard recommendation is IV antibiotics during labor. These reduce the risk of infection by up to 80%.
Pros:
Dramatically lowers chance of serious newborn infection.
Cons:
Alters both mother’s and baby’s microbiome.
Can contribute to antibiotic resistance.
Potential side effects (allergic reaction, yeast imbalance, etc.).
How to Make the Decision
There’s no “one right answer” here. Instead, try reverse engineering your decision:
What outcome matters most to you?
Avoiding a rare but serious infection?
Avoiding unnecessary antibiotics?
What risks feel acceptable to you?
A 1 in 5,000 chance of infection with antibiotics
vs. a 1 in 200 to 1 in 400 chance of infection without antibiotics
What aligns with your birth values?
Trusting natural processes
or prioritizing lowest statistical risk?
The key is knowing you can’t make the risk zero, but you can make a choice that feels right for your family.
Final Thoughts
Group B strep is one of those decisions where knowledge is power. When you understand both the numbers and the trade-offs, you’re no longer at the mercy of “just do the test” or “just skip it.” Instead, you can confidently decide what matters most to you and your baby.
✨ Want more guidance like this?
In my free birth prep class, I walk couples through the exact 10-step system to feel calm and confident for labor—covering how to stay low-risk during pregnancy, comfort techniques for labor, and partner support.
