Group B Strep in Pregnancy: Risks, Testing & Treatment

What Is Group B Streptococcus (GBS)?

Group B Streptococcus (GBS), also known as Streptococcus agalactiae, is a type of bacteria that commonly lives in the intestines, vagina, and rectum of healthy adults. While GBS rarely causes problems for healthy adults, it can be passed from a pregnant woman to her baby during vaginal delivery and potentially cause serious infections in newborns.

Group B Streptococcus is one of many types of bacteria that naturally inhabit the human body without causing illness. Approximately 25-30% of healthy adults carry GBS in their gastrointestinal and genital tracts, a condition known as colonization. Being colonized with GBS is different from having an infection—most people who carry the bacteria never experience any symptoms or health problems.

The bacterium belongs to the Streptococcus family, which includes various species classified by letters (A, B, C, D, etc.). Unlike Group A Streptococcus, which causes strep throat and skin infections, Group B Streptococcus typically doesn't cause disease in healthy adults. However, it has unique significance during pregnancy because of its potential to be transmitted to newborns during childbirth.

GBS can spread from the intestines to the genital area, and during pregnancy, the bacteria can be present in the vaginal canal and rectum. If a mother is colonized with GBS at the time of delivery, there is a possibility that the bacteria can be passed to the baby during a vaginal birth. While GBS can also be transmitted through sexual contact, it is not classified as a sexually transmitted infection (STI) because it naturally occurs in the body and is commonly present without any sexual contact.

Why Is GBS Important During Pregnancy?

The primary concern with GBS during pregnancy is the risk of transmission to the newborn baby during delivery. When a baby passes through the birth canal, they can be exposed to GBS bacteria if the mother is colonized. While most babies who are exposed to GBS remain healthy, a small percentage can develop serious infections that require immediate medical treatment.

Before routine screening and prevention programs were implemented, GBS was a leading cause of severe infections in newborns, including sepsis (bloodstream infection), pneumonia (lung infection), and meningitis (infection of the membranes surrounding the brain). Since the introduction of universal screening and intrapartum antibiotic prophylaxis, the incidence of early-onset GBS disease has decreased by more than 80% in many countries.

GBS and Urinary Tract Infections

While GBS colonization usually causes no symptoms, the bacteria can sometimes cause urinary tract infections (UTIs) in both pregnant and non-pregnant individuals. When GBS is found in urine during routine prenatal testing (a condition called GBS bacteriuria), it indicates significant colonization and is treated with antibiotics during pregnancy.

Common symptoms of a GBS-related UTI include:

• Frequent urge to urinate
• Burning or stinging sensation during or after urination
• Pain in the lower abdomen, above the bladder
• Feeling cold or having chills
• Blood visible in the urine (occasionally)

What Are the Symptoms of GBS Colonization?

Most people with GBS colonization have no symptoms at all. The bacteria can live in the intestines and genital tract without causing any noticeable problems. Symptoms only occur if GBS causes an active infection, such as a urinary tract infection during pregnancy or, rarely, a uterine infection after delivery.

One of the challenges with GBS is that colonization is typically asymptomatic, meaning it causes no symptoms. This is why routine screening during pregnancy is so important—without testing, most women would have no way of knowing they carry the bacteria. GBS colonization can come and go over time, which is why screening is recommended late in pregnancy (36-37 weeks) to accurately reflect GBS status at the time of delivery.

When GBS does cause symptoms, it's usually because the bacteria have caused an active infection rather than simple colonization. The most common GBS-related infection in pregnant women is a urinary tract infection. Less commonly, GBS can cause other infections during pregnancy or after delivery.

Symptoms in Pregnant Women

While GBS colonization itself is silent, certain situations during pregnancy may suggest an active GBS infection or the need for preventive treatment:

• Urinary tract infection symptoms: Burning with urination, frequent urination, lower abdominal pain, or blood in urine
• Fever during labor: Temperature of 38°C (100.4°F) or higher during labor may indicate infection
• Prolonged rupture of membranes: If your water breaks more than 18 hours before delivery, risk of infection increases
• Preterm labor: Labor before 37 weeks increases the importance of GBS prevention

Post-Delivery Complications

In rare cases, GBS can cause infections in the mother after delivery. Postpartum endometritis is an infection of the uterine lining that can occur after childbirth. Symptoms include fever, lower abdominal pain, and abnormal vaginal discharge. This condition requires antibiotic treatment and sometimes hospitalization, but with proper care, most women recover fully within a few days.

When and How Is GBS Testing Done?

Universal GBS screening is recommended for all pregnant women between 36-37 weeks of pregnancy. The test involves taking a simple swab from the vagina and rectum, with results typically available within 24-48 hours. This timing provides accurate information about GBS status at the time of delivery.

GBS screening has become a standard part of prenatal care in many countries around the world. The American College of Obstetricians and Gynecologists (ACOG), the Centers for Disease Control and Prevention (CDC), and numerous other medical organizations recommend that all pregnant women be tested for GBS colonization during their third trimester.

The screening test is simple, quick, and painless. During a prenatal visit, your healthcare provider will use a sterile cotton swab to collect samples from both the vaginal and rectal areas. This sampling technique is important because GBS often colonizes both areas, and testing only the vagina might miss some cases. The swab is then sent to a laboratory where it is cultured to check for the presence of GBS bacteria.

Why 36-37 Weeks?

The timing of GBS screening is carefully chosen for several important reasons:

• Accuracy at delivery: GBS colonization can fluctuate over time. Testing at 36-37 weeks provides the most accurate reflection of your GBS status at the time of delivery.
• Time for planning: Results are available well before your due date, allowing you and your healthcare team to plan for prevention measures during labor.
• Five-week window: Research shows that a negative GBS culture at 36-37 weeks is an excellent predictor of negative status for about 5 weeks, covering most full-term deliveries.

If you go into labor before your scheduled GBS screening, or if your screening was done more than 5 weeks before delivery, your healthcare provider may use a rapid GBS test during labor or treat you based on risk factors.

Understanding Your Results

GBS screening results are typically reported as either positive or negative:

GBS Bacteriuria: A Special Case

If GBS is found in your urine during pregnancy (GBS bacteriuria), this indicates heavy colonization and is treated somewhat differently. Your healthcare provider will prescribe oral antibiotics to treat the urinary infection during pregnancy. Additionally, GBS bacteriuria is considered equivalent to a positive GBS screening result, meaning you will receive intravenous antibiotics during labor even if later vaginal-rectal cultures are negative.

What Are the Risks of GBS to Newborn Babies?

Without prevention, approximately 1-2% of babies born to GBS-colonized mothers develop early-onset GBS disease, which can include sepsis, pneumonia, or meningitis. With intrapartum antibiotics, this risk is reduced by 80-90%. Most babies who become infected can be successfully treated if caught early.

Understanding the risks of GBS to newborns can help parents appreciate why screening and prevention are so important. While the absolute risk to any individual baby is relatively low, the potential consequences of GBS infection can be serious, making prevention efforts worthwhile.

When a baby is exposed to GBS during delivery, most will not become infected. The baby's immune system, combined with protective antibodies passed from the mother during pregnancy, helps fight off the bacteria in the vast majority of cases. However, newborns have immature immune systems, making them more vulnerable to bacterial infections than older children or adults.

Early-Onset GBS Disease

Early-onset GBS disease refers to infections that occur within the first 7 days of life, with most cases appearing within the first 24-48 hours after birth. This is the type of GBS disease that can be prevented through intrapartum antibiotic prophylaxis. Symptoms in affected newborns may include:

• Fever or low body temperature (hypothermia)
• Difficulty feeding or refusal to feed
• Unusual drowsiness or irritability
• Rapid or labored breathing
• Grunting sounds while breathing
• Pale, mottled, or bluish skin color
• Weak cry or decreased activity

The three main types of early-onset GBS disease are:

• Sepsis (blood infection): The most common form, where bacteria enter the bloodstream and spread throughout the body
• Pneumonia: Infection of the lungs, often occurring when the baby inhales infected amniotic fluid or vaginal secretions during birth
• Meningitis: Infection of the membranes surrounding the brain and spinal cord, which can have long-term neurological consequences

Late-Onset GBS Disease

Late-onset GBS disease occurs between 7 days and 3 months of age. Unlike early-onset disease, late-onset GBS disease is not prevented by intrapartum antibiotics, as it results from exposure to GBS after delivery. Sources of late-onset infection can include the mother, other caregivers, or the hospital environment.

Meningitis is more common in late-onset disease compared to early-onset disease. The overall incidence of late-onset GBS disease has remained relatively stable even as early-onset disease has declined due to prevention efforts.

How Is GBS Treated During Pregnancy and Labor?

GBS-positive pregnant women receive intravenous antibiotics during labor, not during pregnancy. The first-line treatment is Penicillin G or Ampicillin, given through an IV starting when labor begins. Antibiotics are most effective when given at least 4 hours before delivery. Women with penicillin allergies receive alternative antibiotics.

The treatment strategy for GBS in pregnancy focuses on preventing transmission to the baby during delivery rather than eliminating GBS colonization during pregnancy. This approach, called intrapartum antibiotic prophylaxis (IAP), has proven highly effective at reducing early-onset GBS disease in newborns.

Research has shown that treating GBS colonization with oral antibiotics during pregnancy is not effective for prevention. The bacteria quickly recolonize the vaginal and rectal areas after treatment ends, meaning the mother would likely be colonized again by the time of delivery. Instead, the most effective approach is to give antibiotics directly into the bloodstream during labor, when the baby is actually at risk of exposure.

How Intrapartum Antibiotics Work

When you arrive at the hospital in labor, if you are GBS-positive or have risk factors for GBS transmission, you will receive intravenous antibiotics. The antibiotics work in two ways:

• Reducing bacterial load: Antibiotics decrease the number of GBS bacteria in the vaginal canal, reducing the baby's exposure during delivery
• Crossing the placenta: Some antibiotic reaches the baby through the placenta and amniotic fluid, providing direct protection

For optimal protection, antibiotics should be given at least 4 hours before delivery. If delivery occurs less than 4 hours after the first dose, the baby will still receive some benefit, though the protection may not be complete. Antibiotics are repeated every 4 hours until delivery to maintain adequate levels.

Antibiotic Choices

The choice of antibiotic depends on your allergy history and the sensitivity of the GBS bacteria:

When Antibiotics Are Given During Labor

You will receive intrapartum antibiotics if any of the following apply:

• You tested positive for GBS at 36-37 weeks
• You had GBS bacteriuria (GBS in urine) during this pregnancy
• You had a previous baby with GBS disease
• Your GBS status is unknown AND you have risk factors (preterm labor, prolonged rupture of membranes, or fever during labor)

How Can GBS Transmission to Babies Be Prevented?

GBS transmission is primarily prevented through universal screening at 36-37 weeks of pregnancy and intravenous antibiotics during labor for those who test positive. This two-step approach has reduced early-onset GBS disease by over 80% since its implementation. There is currently no vaccine available for GBS.

Prevention of GBS disease in newborns relies on a systematic approach that combines identification of at-risk pregnancies with timely treatment during labor. This strategy has been one of the most successful public health interventions in maternal-child health over the past several decades.

The prevention strategy works because GBS transmission almost exclusively occurs during the delivery process. By ensuring that GBS-positive mothers receive antibiotics during labor, the risk of the baby being exposed to large numbers of bacteria is dramatically reduced. The approach is both safe and effective, with minimal side effects for mothers and their babies.

The Two-Step Prevention Strategy

Step 1: Universal Screening

All pregnant women should be tested for GBS colonization between 36-37 weeks of pregnancy. This universal approach ensures that no at-risk pregnancies are missed. The screening test is simple, quick, and covered by most health insurance plans and national health systems.

Step 2: Intrapartum Antibiotic Prophylaxis

Women who test positive for GBS, or who have certain risk factors, receive intravenous antibiotics when they are in labor. Treatment is continued until the baby is delivered to maintain protective antibiotic levels.

Risk-Based Approach When Screening Is Unavailable

In situations where GBS screening results are not available at the time of delivery (for example, if labor begins before the scheduled test), a risk-based approach may be used. Intrapartum antibiotics are recommended if any of the following risk factors are present:

• Preterm labor: Labor beginning before 37 weeks of pregnancy
• Prolonged rupture of membranes: Water breaking more than 18 hours before delivery
• Intrapartum fever: Temperature of 38°C (100.4°F) or higher during labor
• Previous infant with GBS disease: A prior baby who developed GBS infection
• GBS bacteriuria in current pregnancy: GBS found in urine at any point during pregnancy

Future Prevention: GBS Vaccines

Researchers are working on developing vaccines against GBS that could be given to pregnant women to protect their babies. These vaccines would work by stimulating the mother's immune system to produce antibodies that cross the placenta and provide protection to the baby. While several vaccine candidates are in clinical trials, none are currently approved for use. A successful GBS vaccine could eventually eliminate the need for screening and intrapartum antibiotics.

What Happens After the Baby Is Born?

Babies born to GBS-positive mothers are closely monitored for 24-48 hours after birth for any signs of infection. Most babies whose mothers received adequate antibiotics during labor require only routine observation. Babies at higher risk may have blood tests or receive preventive antibiotics.

After delivery, the focus shifts to monitoring the newborn for any signs of GBS infection. The approach to monitoring and any additional testing depends on several factors, including whether the mother received antibiotics, how long before delivery the antibiotics were given, and whether the baby shows any symptoms.

For most babies born to GBS-positive mothers who received adequate intrapartum antibiotics (at least 4 hours before delivery), routine monitoring is sufficient. Healthcare providers will watch for any signs of infection during the first 24-48 hours after birth. If the baby appears healthy and shows no concerning symptoms, no additional testing or treatment is typically needed.

Newborn Observation

All newborns are observed for vital signs and general well-being after birth, but babies born to GBS-positive mothers receive particularly close attention. Healthcare providers monitor for:

• Temperature stability (fever or hypothermia)
• Respiratory rate and effort
• Feeding behavior and ability
• Activity level and alertness
• Skin color and perfusion

Parents are also educated about signs of infection to watch for after going home, particularly in the first week of life. If a baby develops any concerning symptoms, parents should seek medical attention immediately.

When Additional Evaluation Is Needed

In certain situations, additional evaluation or treatment may be recommended for the newborn:

• Inadequate intrapartum prophylaxis: If antibiotics were given less than 4 hours before delivery, the baby may need closer observation or blood tests
• Signs of infection in the baby: Any symptoms suggestive of infection warrant immediate evaluation, including blood cultures and possible empiric antibiotic treatment
• Chorioamnionitis in the mother: If the mother had signs of infection of the amniotic fluid, the baby is at higher risk and typically receives blood tests and observation
• Preterm birth: Premature babies have less developed immune systems and may require additional monitoring or preventive treatment

What If GBS Is Found in Urine During Pregnancy?

GBS found in urine (GBS bacteriuria) indicates heavy colonization and requires antibiotic treatment during pregnancy to prevent urinary tract complications. Women with GBS bacteriuria are automatically considered GBS-positive for labor and will receive intravenous antibiotics during delivery, regardless of later screening results.

When routine urine tests during prenatal care detect GBS bacteria, this finding has important implications for pregnancy management. GBS bacteriuria occurs in approximately 2-7% of pregnant women and indicates that there is a significant amount of GBS bacteria present in the urinary tract.

Unlike simple GBS colonization of the vagina and rectum (which is not treated during pregnancy), GBS bacteriuria requires treatment for two reasons. First, the presence of bacteria in the urine can lead to urinary tract infections that may progress to kidney infections if left untreated. Second, GBS bacteriuria is associated with higher levels of vaginal and rectal colonization, increasing the risk of transmission to the baby during delivery.

Treatment During Pregnancy

If GBS is found in your urine, your healthcare provider will prescribe oral antibiotics to treat the bacteriuria. The specific antibiotic and duration of treatment depend on the sensitivity of the bacteria and your individual health situation. It's important to complete the full course of antibiotics even if you feel fine, as undertreating can lead to recurrence or antibiotic resistance.

Impact on Delivery Planning

Having GBS bacteriuria at any point during pregnancy automatically qualifies you for intrapartum antibiotic prophylaxis. This means you will receive IV antibiotics during labor, even if a later vaginal-rectal culture comes back negative. The reasoning is that GBS bacteriuria indicates heavy colonization, and a single negative swab might miss the presence of bacteria.

What Are Special Situations That Affect GBS Management?

Several situations require modified GBS management, including preterm labor, prolonged rupture of membranes, penicillin allergy, and planned cesarean delivery. Healthcare providers adjust their approach based on these specific circumstances to optimize protection for both mother and baby.

While the basic principles of GBS prevention remain consistent, certain clinical situations require healthcare providers to modify their approach. Understanding these special circumstances can help pregnant women prepare for different scenarios and have informed discussions with their healthcare team.

Preterm Labor (Before 37 Weeks)

Women who go into labor before 37 weeks of pregnancy present a unique challenge because they may not have had their GBS screening yet. In this situation, if GBS status is unknown, intrapartum antibiotics are given because:

• Premature babies have less developed immune systems and are more vulnerable to infection
• There isn't time to wait for culture results
• The consequences of GBS infection in preterm infants can be more severe

Prolonged Rupture of Membranes

When the amniotic membranes rupture (water breaks) more than 18 hours before delivery, the risk of GBS transmission increases. The protective barrier provided by the membranes is gone, allowing bacteria to potentially ascend into the uterus. Women with prolonged rupture of membranes and unknown GBS status should receive intrapartum antibiotics as a precaution.

Penicillin Allergy

For women with penicillin allergies, alternative antibiotics are available for GBS prophylaxis. The choice of alternative antibiotic depends on the type and severity of the allergy:

• Non-severe allergy (rash only): Cefazolin is typically safe and effective
• Severe allergy (anaphylaxis, hives, respiratory symptoms): Clindamycin or vancomycin may be used, depending on antibiotic susceptibility testing

If you have a penicillin allergy, it's important to discuss this with your healthcare provider early in pregnancy. In some cases, the GBS bacteria found during screening will be tested for susceptibility to clindamycin to guide treatment choices.

Planned Cesarean Delivery

Women having a planned cesarean section before labor begins and before rupture of membranes generally do not need GBS prophylaxis. Since the baby is delivered surgically without passing through the birth canal, the primary route of GBS transmission is eliminated. However, if labor has already started or the membranes have ruptured, GBS prophylaxis should be given regardless of planned delivery method.