Group B Strep Colonization and Pregnancy

At Mon Aug 20, 11:32:00 AM 2007, Anonymous said…


Hi there Dr. T. I am 36 1/2 weeks and I just found out that I was GBS+ and I am very concerned about my baby. I wonder, why give antibiotics during labor? Why not now? I have also had many problems with yeast infections during my pregnancy and was wondering if that could have caused the GBS? I don't completely understand why I have it and what I did to get it. Is it caused from something, perhaps the heat? Not being clean enough? Please help me!


One of my very first posts here at “Fruit of the Womb” addressed Group B Streptococcus (GBS) infections and pregnancy. The question from today’s reader gives us good reason to revisit this issue since the concerns expressed in the comment are shared by many, many women....

GBS is a bacterium that colonizes the vagina and lower gastrointestinal tract in as many as one-third of all healthy reproductive age women. It is still the leading cause of serious bacterial infection in newborns and most babies contract the organism at the time of delivery. Indeed, 8,000-12,000 babies per year in the U.S. will develop complications related to GBS and approximately 2,000 infants will die from their infections. There are several well-known situations in which babies are at increased risk for developing a serious GBS infection including:

• Premature labor or rupture of membranes before 37 weeks
• Prolonged rupture of membranes (18 hr or longer) before delivery
• Fever in labor (100.4F or higher)
• History of GBS urinary tract infection during the pregnancy (4-fold risk)
• Previous baby affected by GBS disease (increases risk 10-fold!!!)

Some of the dilemmas we face in dealing with GBS in pregnancy are raised by today’s reader. She appears to have had GBS detected at the time of recommended routine screening, 35-37 weeks. She didn’t just “catch it” at this point; it is probably something she has carried with her through most of the pregnancy (and even before conception). We do NOT know why some people carry GBS and others do not, and we are not entirely clear why far more women actually carry the bacterium than are at risk for having a baby with a serious complication related to it, although the maternal immune response to the bacterium probably plays a key role (see below). But, we also know that if you are colonized with GBS and tend to carry it, even if treated, you have a very high risk of being incompletely ‘decolonized’ by treatment and a similarly high risk for becoming ‘recolonized’ in a relatively short period of time for whatever reasons you have it to begin with!

GBS may come and go, but a negative test within 5 weeks of delivery has a ‘negative predictive value’ of about 95%. This implies that only 5% of women who are negative at 35-37 weeks are likely to acquire GBS between the time of screening and delivery. Interestingly, if GBS is detected at routine screening, the ‘positive predictive value’ of the bacteria actually being found at delivery is only about 87%. This means that as many as 13% of women who were positive at the time of screening will not have the bacterium detectable at the time of delivery.

To answer some of our reader’s concerns, these are reasons we do not treat everyone at the time a positive screening test is done unless they themselves have a significant infection (e.g., urinary tract), a previously affected baby, or are in one of the other risk categories noted above. According to the CDC, women who are GBS positive have about a 50% of having a baby who becomes colonized with GBS at delivery and a 1 in 200 chance of having a baby who develops GBS disease if antibiotics are NOT given, but only 1 in 4000 risk if they are given.

There are 5 major serotypes of GBS (Ia, Ib, II, III, and V). All are capable of causing both maternal and neonatal disease. Babies born to women who do not have antibodies to types II and III seem to be at greater risk for complications. Indeed, at some point, this may be one of the primary factors we can use to differentiate pregnancies at risk from those which are less so. About two-thirds of serious GBS infections are apparent at the time of delivery and 90% of babies who will develop complications do so within the first 48 hr after delivery. This is generally referred to as “early-onset” GBS infection and technically is used to define disease occurring in the first week of life. “Late-onset” disease, frequently associated with serotype III, affects another 10% of newborns, often presents as meningitis with septicemia, and rarely occurs after one month of age. Up to one-third of the survivors of GBS meningitis will develop long-term physical and/or neurological handicaps and in 1 of every 8 of these babies, the handicaps will be severe.

Unless you are in one of the high risk groups noted above, the goal of routine prophylactic antibiotic therapy during labor in those who are found to be colonized with GBS during their pregnancies is to deliver antibiotics to the mother early enough in the course of labor that sufficient drug can be transferred across the placenta to achieve protective levels in the baby prior to birth. The goal is not to cure the GBS infection. That means, the antibiotic selected must not only be able to kill GBS, but it must also be able to cross the placenta. Fortunately, GBS has not yet been found to have developed resistance to the antibiotic of choice, penicillin G, and this drug also readily crosses the placenta. It also has a long and proven safety record for the baby. Ideally, antibiotic therapy is begun, intravenously, at least 4 hr prior to delivery so that at least one or two doses can be administered before the baby is born. If a woman has a serious allergy to penicillin, other otions for therapy exist and the risks and benefits of these are discussed in our previous post on this subject.

Anyway, to close this out, I would only like to say to our reader that 1) I doubt the recurrent yeast infections “caused” the GBS, but they might reflect a subtle deficiency in your immune response to other organisms commonly found in the environment. (People with diabetes and autoimmune conditions frequently experience similar problems or, in your case, this may be simply the response your body has to pregnancy; 2) I don’t completely understand why you have it either, but I doubt the “heat” is contributing to the problem and cleanliness is rarely a concern in people who would worry about that to begin with!

The important things are that your doctors did the right thing by screening you, they have identified a potential problem, and there is a well-proven means of significantly reducing the risks from that problem for both you and your baby at the time of your labor and delivery. Thanks for reading and for the good questions. Best wishes for the rest of your pregnancy!

Dr T on Aug 20, 11:32:00 AM 2007