Should I Take Antibiotics for Group B Strep During Pregnancy?

Hello! I’m wondering about the risks vs. benefits of antibiotics during labor for group B strep (GBS)? I’m usually very comfortable with a medicalized model and birth, but I also just tested positive for GBS at 36 weeks and read about the negative impact of killing off good bacteria for the baby at that stage (during labor/birth). Thank you!
—GBS-positive questioning

It is useful to start with why antibiotics are used during labor in this case. Group B strep (GBS) is a common bacterial infection that is often asymptomatic, but it can be extremely dangerous in infants less than four weeks old. About 1 in 2,000 neonates have GBS infections, which can manifest in respiratory distress, sepsis, or meningitis within the first week of life. This can be very dangerous, in some cases leading to infant death.

In the U.S., all women are screened for GBS late in pregnancy, and if they are positive, the standard treatment is antibiotics during labor. The idea is that this will lower the bacterial load and decrease the risk of infection being passed to the infant.

This approach is based on data from several relatively small randomized trials. A 2014 Cochrane Review summarizes them. In total, only 852 women were included across four trials, only three of which compared antibiotic treatment with no treatment. The trials are now all more than 20 years old. When the authors of the review combine the trials together, they draw two main conclusions. First, treatment with antibiotics appears to lower the risk of GBS infection (by about 80%). Second, there is no statistically significant reduction in neonatal mortality in these trials.

The authors of the review are somewhat skeptical about these treatments based on this evidence, but it seems worth noting to me that given how rare neonatal mortality is (thankfully), the trials are statistically underpowered to learn anything about that outcome. With only several hundred babies, the anticipated number of deaths is extremely small. And over time, as universal screening for GBS has been introduced, we have seen the incidence of infection fall and mortality has also fallen. This isn’t randomized, but it is at least supportive of efficacy, combined with the evidence on GBS infection.

In an ideal world, we would have better randomized evidence on the question of mortality, but the reality is it will be hard to learn more about this relationship with randomized trials at this point. This treatment is the accepted standard of care, so ethically, randomization is unlikely to be approved. Based on what we do see, it seems likely to me that there is some effect, but it is probably fairly small.

The downsides to antibiotics are concerns about overuse, yeast infections, and allergic reactions. There are also various concerns expressed about changes in the microbiome, but these are difficult to quantify and it is hard to know their impact.

What should you do? The reality is you may not have a choice here. This treatment is extremely standard, and probably for good reason.