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Welcome back for another episode of the OB GYN Resident Survival Guide, a podcast with bite sized clinical pearls that you can consume on the run. I'm Dr. Miller, an OB GYN and the host of this show. This week's episode is all about GBS Prophylaxis in labor. Before I jump in, I have two reminders. Number one, the free obgyn Intern Starter Pack is available for download for those of you preparing to start residency on July 1st. And number two, because people have been asking yes, the doors to OB GYN Residency Boot Camp will be opening again this spring. OB GYN Residency Bootcamp is the crash course I wish I had prior to starting residency. It's five modules long and provides clear frameworks for managing labor, triage, postpartum care, guiding emergencies, and an intro to clinic. Inside the course, we focus on practical decision making, common scenarios, and step by step approaches to OB and gyncare that new interns face every day throughout their first year of training. Enrollment opens again this spring and the link to join the waitlist is in the show. Notes if you're interested all right, let's get started. Gbs, short for Group B streptococcus, is a normal component of the GI and vaginal microbiome in many patients. About 10 to 30% of pregnant patients will have colonization in the vagina and or the rectum, and of those patients at the about 50% will transmit that bacteria to their newborns during labor or following membrane rupture. If untreated, about 1 to 2% of those newborns will later develop GBS early onset disease, which is characterized by sepsis, pneumonia or meningitis within seven days of birth. And although that percent seems pretty low, this is actually the leading cause of neonatal sepsis in the early newborn period. So the GBS prophylaxis protocol that we'll be talking about today was developed with the goal of reducing the risk for GBS early onset disease in the neonates. First, I'm going to talk about the who, and then I'm going to talk about the how. So patients should receive GBS prophylaxis if they fall into either of two categories. One they've tested positive for GBS at some point in the pregnancy or two we don't know what their GBS status is, but they're preterm or have risk factors for colonization. So let's break it down. Firstly, patients are considered to be colonized with GBS if they have had a positive rectovaginal culture, which we typically collect at or after 36 weeks gestation of pregnancy or if they developed GBS bacteria at any time during the pregnancy. And this is because GBS bacteriuria symptoms suggests heavy rectovaginal colonization, which therefore increases the risk of GBS transmission to the neonate. Secondly, for patients whose GBS status is unknown, we recommend treatment if they are preterm or have specific risk factors for colonization. So as a reminder, preterm is defined as a gestational age less than 37 weeks and 0 days gestation. Risk factors for colonization include prolonged rupture of membranes, so that would be 18 hours or greater the development of an intrapartum maternal fever which would be 38 degrees Celsius or 100.4 degrees Fahrenheit. Additionally, a history of being GBS positive in a prior pregnancy or a prior pregnancy with a neonate that was known to be affected by GBS early onset disease. Lastly, this isn't necessarily a risk factor, but some hospital institutions will offer nucleic acid amplification testing in labor for gbs. If your facility offers that and the test is positive for gbs, these patients should be treated. However, if the test is negative but they're preterm or have any of the previously mentioned risk factors, prophylaxis should be administered anyway. So that's the whole now let's talk about the how the standard antibiotic regimen for DBS prophylaxis as supported by the American College of Obstetricians and Gynecologists, is IV penicillin G or IV ampicillin, depending on your institutional protocol and pharmacy availability. Regardless of the antibiotic being used, treatment should be initiated at least four hours before the anticipated delivery and continued until birth. The regimens I'm reviewing today are up to date as of January 2026. And as a disclaimer, although I will be reviewing the recommended dosing regimens in this protocol, this podcast episode is really just meant for your review. This should not be your primary source when trying to determine how to place your orders for your patients. If you're trying to figure out what dosing regimen to put your patients on, please refer to your own specific hospital protocol or reach out to your pharmacist as well as directly referencing the ACOG practice guidelines that are listed in the references. All right, so now that's out of the way, let's jump into the regimen. Our first line treatment options are IV penicillin G and ampicillin IV for pen G. We start with a loading dose of 5 million units followed by 2 and a half to 3 million units every four hours until delivery. For IV ampicillin, the recommended dose is a loading dose of 2 grams followed by 1 gram every 4 hours until delivery. It gets a little bit trickier when choosing a regimen for patients with a penicillin allergy because we have to determine how severe their allergy really is. There's a great table listed in the ACOG Practice bulletin referenced in the show notes that breaks this down. But in summary, a high risk penicillin allergy is defined as a prior reaction that presented with anaphylaxis, hives, a pruritic rash, angioedema, flushing, hypotension or respiratory distress. But go check out that chart for a full review. So let's talk about patients with low risk allergies and then high risk allergies. If a patient has a low risk allergy, meaning not anaphylaxis, hives, itching, rash, angioedema, flushing, hypotension or respiratory distress, we can treat those patients with cefazolin. The Recommendation is a 2 gram IV loading dose followed by 1 gram IV every 8 hours until delivery. For patients with a high risk penicillin allergy, meaning history of anaphylaxis, hives, itching, rash, angioedema, flushing, hypotension and or respiratory distress. We can use either clindamycin or vancomycin and the one that you choose depends on whether or not your lab ran clindamycin susceptibility testing on the rectovaginal culture collected in clinic or or the urine specimen that demonstrated bacteriurea. So it's really important that when you're placing the GBS culture order in clinic after you've collected the specimen that you enter into the order comments that the patient is pregnant and has a known penicillin allergy so that the lab is aware and then can test the isolate for clindamycin resistance. If the isolate is susceptible to clindamycin then we can treat these moms with clindamycin not 900mg IV every eight hours until delivery. And if the isolate is resistant to clindamycin or susceptibility testing was never done or you don't have the results, then we would treat with weight based vancomycin iv. Alright, so that's the WHO and the how. But before I wrap up I do want to mention two points. Firstly, GBS positive patients undergoing a pre labor cesarean do not need GBS prophylaxis so long as their membranes are intact prior to the procedure. Now, the Practice Bulletin and Gabby's Obstetrics don't comment specifically on patients whose membranes are intact but are in labor and needing a cesarean. The greatest predictor for transmission is membrane status, because if the membranes are intact, this provides a barrier between the lower genital tract and amniotic cavity. That being said, if you have a patient that comes into triage huffing and puffing with a breech fetus, they're known GBS positive, their membranes are intact, and it might be an hour or two or more before you have an available operating room or anesthesia available to take the patient back for cesarean. Your attending may recommend initiating prophylaxis just in case because it's a bit of a gray area, but generally, so long as the membranes are intact, risk of transmission is low. The second point I want to make is that a negative rectovaginal culture result is valid for five weeks from collection. So if you have a patient that had a GBS culture result at 36 weeks and 0 days that somehow manages to stay pregnant beyond 40 weeks, it's important to repeat the rectovaginal culture to confirm that it is still negative. All right, let's recap it all. The goal of intrapartum GDS prophylaxis is is to reduce the risk of GBS early onset disease in the neonate. We treat mothers in labor if they have had a positive rectovaginal culture or GBS bacteriuria during the pregnancy. Additionally, if the results of GBS testing are unknown, we administer prophylaxis if they are preterm, have had prolonged rupture of membranes, the presence of a maternal fever, history of GBS colonization in a prior pregnancy, history of GBS early onset disease, the neonate in a prior pregnancy and or if they have had a positive nucleic acid amplification test. Collected intrapartum prophylaxis with penicillin G IV or ampicillin IV is preferred. However, if the patient is allergic to penicillin, we can offer cefazolin, clindamycin or vancomycin depending on the severity of their allergy and the results of clindamycin susceptibility testing. A negative rectovaginal culture result is valid for five weeks. After that, a repeat culture should be collected. And lastly, GBS positive patients that are undergoing cesarean do not require prophylaxis so long as their membranes are intact prior to the procedure. That's it for today. As usual, the references are listed in the show notes, along with the links to the OB GYN Intern Starter Pack and the OBGyn Residency Boot Camp wait list. I'll see you next week.