Vaginal infections during pregnancy exist in a category of concerns that feel both minor and potentially serious. On one hand, they’re incredibly common and usually treatable with simple antibiotics. On the other, certain infections can affect pregnancy outcomes in ways that matter significantly for the baby’s health. Bacterial vaginosis falls squarely into this complicated middle ground.

BV is the most common cause of abnormal vaginal discharge in women of childbearing age, affecting 10% to 30% of pregnant women in the United States. That’s potentially one in three pregnancies. For many women, it causes no symptoms at all and resolves without treatment. For others, particularly those with certain risk factors, bacterial vaginosis is associated with preterm birth, low birth weight, and other complications that can affect a baby’s immediate and long-term health.

Understanding bacterial vaginosis during pregnancy means knowing what it is, recognizing when it requires treatment, understanding the real risks it poses, and knowing how to reduce the chance of developing it. This article examines the science behind BV in pregnancy, its connection to pregnancy complications, current screening and treatment recommendations, and practical information for women who are pregnant or planning to become pregnant.

What Bacterial Vaginosis Is and How It Differs From Other Infections

Bacterial vaginosis isn’t caused by a single invading bacteria the way strep throat comes from Streptococcus bacteria. It’s an imbalance in the vaginal ecosystem, a shift in the types and numbers of bacteria naturally present in the vagina.

The Normal Vaginal Microbiome

A healthy vagina contains a complex community of bacteria, predominantly Lactobacillus species. These beneficial bacteria maintain an acidic environment that protects against harmful bacteria and infections. Lactobacilli produce lactic acid and hydrogen peroxide, creating conditions where most potentially harmful organisms can’t thrive.

The vaginal pH in healthy women is typically between 3.8 and 4.5, acidic enough to suppress most problematic bacteria while allowing the beneficial Lactobacillus species to flourish. This delicate balance is the vagina’s natural defense system against infection.

What Happens When Bacterial Vaginosis Develops

In bacterial vaginosis, the population of protective Lactobacillus bacteria decreases dramatically, and other bacteria overgrow to fill the void. These include Gardnerella vaginalis, Prevotella species, Mobiluncus species, and various anaerobic bacteria that don’t require oxygen to survive.

The shift in bacterial population changes the vaginal pH, making it less acidic and more alkaline, typically rising above 4.5. This pH change allows even more problematic bacteria to thrive, creating a self-reinforcing cycle. The overgrown bacteria produce compounds that cause the characteristic symptoms when they’re present.

Importantly, BV isn’t a sexually transmitted infection in the traditional sense, though sexual activity can contribute to its development. It’s not something you “catch” from a partner. Rather, it’s a disruption of your own bacterial balance.

How BV Differs From Yeast Infections and STIs

Women sometimes confuse BV with yeast infections or sexually transmitted infections because they can all cause vaginal discharge and discomfort. But they’re distinct conditions:

Yeast infections are caused by fungal overgrowth, typically Candida species, and cause thick white discharge, intense itching, and burning. BV causes thin discharge with a fishy odor but often less itching.

Sexually transmitted infections like chlamydia, gonorrhea, or trichomoniasis are caused by specific pathogens transmitted during sex and require different treatments. Some STIs cause symptoms similar to BV, which is why proper diagnosis matters.

The distinction is important because treatments differ and because the pregnancy risks associated with these conditions vary.

How Common Bacterial Vaginosis Is During Pregnancy

Bacterial vaginosis isn’t rare. It’s one of the most common conditions affecting pregnant women, though many don’t realize they have it.

Prevalence Rates in Pregnant Women

Research consistently shows that 10% to 30% of pregnant women have bacterial vaginosis at some point during pregnancy. The CDC estimates approximately one million cases annually in the United States. This makes BV more common than many pregnancy complications that receive more attention.

The wide range in prevalence estimates reflects several factors: different study populations, varying definitions of BV, whether studies screen all pregnant women or only those with symptoms, and differences in risk factors across populations studied.

Why Many Women Don’t Know They Have BV

A substantial percentage of women with bacterial vaginosis have no symptoms. Studies suggest that up to half of women with BV confirmed by testing report no symptoms prompting them to seek care.

This asymptomatic presentation creates a challenge. Women without symptoms don’t know they have BV unless they’re screened as part of research studies or targeted screening programs. This means many women with BV go through entire pregnancies without diagnosis or treatment, which raises questions about whether universal screening would improve outcomes.

Population Differences in BV Rates

BV rates aren’t uniform across all groups. Research shows higher rates among Black and Hispanic women compared to white women, and higher rates in women with lower socioeconomic status. These disparities likely reflect multiple factors including differences in the vaginal microbiome, environmental exposures, stress, nutrition, and access to healthcare.

Understanding these disparities is important for identifying who might benefit most from screening and treatment programs.

Symptoms of Bacterial Vaginosis and How to Recognize It

When bacterial vaginosis does cause symptoms, they’re usually distinctive enough to recognize, though they’re often mistaken for other conditions.

The Characteristic Fishy Odor

The most notable symptom of BV is a fishy or musty vaginal odor. This smell comes from amines produced by the overgrown bacteria. The odor is often stronger after sexual intercourse because semen is alkaline and releases more of these amine compounds.

Many women find this symptom embarrassing and may delay seeking care, but it’s a medical symptom like any other and one that healthcare providers address routinely.

Changes in Vaginal Discharge

BV typically causes increased vaginal discharge that’s thin and grayish-white or gray-green in color. The discharge is usually watery rather than thick or cottage-cheese-like, distinguishing it from yeast infections.

The amount of discharge varies. Some women notice only slightly more than usual, while others have significant discharge requiring frequent pad changes.

Other Symptoms That May Occur

Additional symptoms can include:

Mild itching or irritation, though this is less prominent than with yeast infections
Burning during urination, though less common than with urinary tract infections
General vaginal discomfort

When BV Causes No Symptoms At All

Many women with BV experience no symptoms whatsoever. The bacterial imbalance exists, can be detected through testing, and carries the same pregnancy risks as symptomatic BV, but produces no discharge, odor, or discomfort alerting the woman to the problem.

This is why screening is sometimes recommended for women at high risk for preterm birth, even when they have no symptoms suggesting infection.

The Connection Between BV and Preterm Birth

The most significant concern about bacterial vaginosis during pregnancy is its association with preterm birth, delivery before 37 weeks of pregnancy.

How BV Increases Preterm Birth Risk

Research consistently shows that women with bacterial vaginosis during pregnancy have approximately double the risk of preterm birth compared to women without BV. In one large prospective study, the preterm birth rate among women with BV was 22.7% compared to 6.2% in women without BV.

The mechanism connecting BV to preterm birth involves inflammation and immune responses. The bacteria associated with BV produce enzymes and inflammatory compounds that can:

Weaken fetal membranes, increasing the risk of premature rupture
Trigger inflammatory responses in the uterus and cervix
Cause the body to release prostaglandins and cytokines that can stimulate contractions
Lead to subclinical infections of the amniotic fluid or membranes

These processes can initiate preterm labor or cause membranes to rupture before term, leading to early delivery.

The Earlier in Pregnancy, The Greater the Risk

Evidence suggests that BV earlier in pregnancy, particularly in the first and second trimesters, carries higher risk for preterm birth than BV detected late in pregnancy. This timing makes sense given that prolonged exposure to the inflammatory effects of BV would have more opportunity to affect pregnancy.

This also explains why screening programs often focus on the first or early second trimester, attempting to identify and treat BV before it can contribute to preterm birth.

Individual Risk Varies Based on Other Factors

Not every woman with BV delivers preterm. The absolute risk remains relatively low for many women, but certain factors increase vulnerability:

Prior preterm birth history significantly increases risk
Multiple bacterial infections or severe BV increases risk
Other risk factors for preterm birth like short cervix or multiple pregnancy compound the risk
Individual immune responses and inflammatory tendencies vary

This is why screening and treatment recommendations focus on women with prior preterm births who face the highest risk.

Other Pregnancy Complications Associated With Bacterial Vaginosis

Beyond preterm birth, BV is linked to several other pregnancy complications affecting both mother and baby.

Low Birth Weight and Growth Restriction

Babies born to mothers with BV have higher rates of low birth weight, defined as less than 5 pounds, 8 ounces at birth. This occurs partly through preterm birth, since babies born early naturally weigh less, but also through direct effects on fetal growth.

The inflammation associated with BV may affect placental function, potentially limiting nutrient and oxygen delivery to the fetus. This can result in growth restriction where babies are smaller than expected even if delivered at term.

Premature Rupture of Membranes

Premature rupture of membranes, when the amniotic sac breaks before labor begins, occurs more frequently with BV. The bacteria and their enzymes can weaken the membranes, making them more likely to rupture.

When membranes rupture preterm, before 37 weeks, it often leads to preterm delivery. Even when rupture occurs at term, it increases the risk of infection since the protective barrier of intact membranes is lost.

Miscarriage Risk

Some research suggests BV may increase the risk of late miscarriage, though the evidence is less clear than for preterm birth. The same inflammatory processes that can trigger preterm labor might contribute to pregnancy loss before viability.

Postpartum Infections

Women with BV during pregnancy have higher rates of endometritis, infection of the uterine lining after delivery. This occurs because the bacteria associated with BV can ascend into the uterus during labor and delivery, establishing infection in the postpartum period.

Endometritis causes fever, abdominal pain, and foul-smelling discharge after delivery. It requires antibiotic treatment and sometimes hospitalization.

Neonatal Complications

Babies born to mothers with BV face higher rates of complications including:

Respiratory distress requiring breathing support
Higher admission rates to neonatal intensive care units
Longer hospital stays after birth
Potential exposure to bacteria during delivery
Slightly higher rates of neonatal infection

Many of these complications relate to preterm birth rather than direct bacterial effects, but the overall impact on newborn health is measurable.

How Bacterial Vaginosis Is Diagnosed During Pregnancy

Proper diagnosis of BV requires medical evaluation, as women can’t reliably self-diagnose based on symptoms alone.

Clinical Diagnosis Using Amsel Criteria

Healthcare providers often diagnose BV using clinical criteria. The Amsel criteria require three of four findings:

Thin, gray-white vaginal discharge
Vaginal pH greater than 4.5, measured with pH paper
Positive “whiff test” where a fishy odor is detected when potassium hydroxide is added to a sample of discharge
Presence of clue cells, which are vaginal epithelial cells covered with bacteria, seen under microscopy

This clinical approach provides immediate diagnosis during the office visit.

Laboratory Testing Methods

Laboratory testing offers more definitive diagnosis. Options include:

Gram stain of vaginal fluid, examining the types and quantities of bacteria present
Nugent score, a standardized scoring system based on Gram stain findings
DNA-based tests identifying specific bacteria associated with BV
Culture of vaginal fluid, though less commonly used for BV

These tests are particularly useful when diagnosis is uncertain or for research purposes.

Why Self-Diagnosis Isn’t Reliable

Women sometimes attempt to self-diagnose BV based on symptoms, but this is unreliable because:

Other infections cause similar symptoms
Some women with BV have no symptoms
Symptoms can be vague or misinterpreted
Proper diagnosis requires pH testing and microscopy

Professional diagnosis ensures accurate identification and appropriate treatment.

When Testing Is Recommended

Testing for BV is recommended when:

A pregnant woman has symptoms of vaginal discharge, odor, or irritation
A woman with prior preterm birth is pregnant again, even without symptoms
Evaluation is being done for another vaginal infection
A woman is experiencing preterm labor and BV is being considered as a contributing factor

Current Screening Recommendations for Pregnant Women

Medical organizations have established guidelines about who should be screened for BV during pregnancy, balancing potential benefits against costs and intervention risks.

Why Universal Screening Isn’t Recommended

The U.S. Preventive Services Task Force, after reviewing extensive evidence, does not recommend routine screening of all pregnant women for BV. This recommendation reflects several considerations:

Studies of screening and treating asymptomatic BV in low-risk women haven’t shown consistent reduction in preterm birth. Treating all women with asymptomatic BV would expose many to antibiotics without clear benefit. The cost of universal screening programs would be substantial.

This doesn’t mean BV isn’t important. It means that for most pregnant women without symptoms or risk factors, screening hasn’t proven beneficial enough to recommend for everyone.

Who Should Be Screened

Screening is recommended for:

All pregnant women with symptoms of BV
Women with a history of preterm birth in previous pregnancies
Women undergoing evaluation for preterm labor
Possibly women with other risk factors for preterm birth, though this is more controversial

The focus on women with prior preterm birth reflects evidence that this group benefits most from identification and treatment of BV.

Timing of Screening for High-Risk Women

For women with prior preterm birth, screening is typically done in the first trimester or early second trimester, ideally before 20 weeks of pregnancy. Earlier detection and treatment theoretically provides more opportunity to prevent the inflammatory cascade that contributes to preterm birth.

The Debate About Screening Practices

The screening recommendations remain somewhat controversial. Some experts argue that broader screening could identify more cases and potentially reduce preterm birth rates, particularly in high-risk populations. Others emphasize that evidence doesn’t support screening low-risk women and that resources might be better spent on other interventions.

This ongoing debate reflects the complexity of BV, the multifactorial nature of preterm birth, and challenges in designing definitive studies.

Treatment of Bacterial Vaginosis During Pregnancy

When BV is diagnosed during pregnancy, treatment decisions depend on whether the woman has symptoms and her risk factors for preterm birth.

Antibiotic Treatment Options

BV is treated with antibiotics effective against the anaerobic bacteria that overgrow in this condition. Options include:

Metronidazole, given orally or as vaginal gel. Oral metronidazole is typically prescribed as 500 mg twice daily for 7 days, or 250 mg three times daily for 7 days. The vaginal gel is applied once or twice daily for 5 days.

Clindamycin, available as oral capsules or vaginal cream. The oral form is typically 300 mg twice daily for 7 days. Vaginal cream is applied at bedtime for 7 days.

Both medications are considered safe during pregnancy, though some providers prefer to avoid metronidazole in the first trimester if possible, using clindamycin instead.

Treatment for Symptomatic Pregnant Women

All pregnant women with symptomatic BV should be treated, according to CDC guidelines. The treatment:

Relieves uncomfortable symptoms
May reduce the risk of preterm birth, though evidence is mixed
Reduces risk of postpartum infections
Prevents potential spread of bacteria to the upper reproductive tract

Treatment course should be completed even if symptoms resolve before completion.

Treatment for Asymptomatic Women With Prior Preterm Birth

For women without symptoms but with a history of preterm birth, treatment is generally recommended even though evidence of benefit is not definitive. The rationale is that this high-risk group might benefit from BV treatment even if average-risk women don’t.

Treatment for Asymptomatic Low-Risk Women

For women without symptoms and without prior preterm birth, treatment is typically not recommended even if BV is incidentally detected. The evidence doesn’t show that treating asymptomatic low-risk women prevents adverse outcomes, and treatment could potentially cause side effects without benefit.

Follow-Up After Treatment

Routine test-of-cure is not recommended after completing treatment in most cases. However, follow-up testing might be considered for:

Persistent symptoms despite treatment
Women with prior preterm birth to confirm cure
If symptoms recur suggesting treatment failure or reinfection

The Problem of Recurrence

BV frequently recurs even after successful treatment. Recurrence rates within months of treatment are high, sometimes exceeding 50%. This happens because:

Treatment kills bacteria but doesn’t necessarily restore the normal Lactobacillus population
Underlying factors promoting BV may persist
Sexual activity can reintroduce disruption
The vaginal ecosystem doesn’t automatically rebalance

Recurrent BV can be frustrating and may require repeated treatment courses or alternative management strategies.

Preventing Bacterial Vaginosis During Pregnancy

While not all cases of BV are preventable, certain practices reduce risk.

Why Douching Increases BV Risk

The single most important modifiable risk factor for BV is douching. Douching disrupts the normal vaginal microbiome by:

Washing away beneficial Lactobacillus bacteria
Changing vaginal pH
Potentially introducing new bacteria
Creating an environment where problematic bacteria can flourish

Women who douche regularly have significantly higher rates of BV than women who don’t douche. Healthcare providers universally recommend against douching, particularly during pregnancy.

Sexual Practices and BV Risk

Sexual activity affects BV risk in several ways:

Having new or multiple sexual partners increases risk
Sexual activity can introduce substances and bacteria disrupting vaginal pH
Semen is alkaline and temporarily raises vaginal pH
Some research suggests female sexual partners increase risk more than male partners

Using condoms may reduce BV risk, though evidence is mixed. The protective effect might come from reduced exposure to semen or from prevention of STIs that could contribute to vaginal imbalance.

Hygiene Practices That Don’t Increase Risk

Normal external washing with mild soap and water doesn’t increase BV risk. Women don’t need special products or extensive cleaning routines. The vagina is self-cleaning, and normal bathing is sufficient.

Avoid:

Scented feminine hygiene products
Vaginal deodorants or perfumed products
Harsh soaps in the vaginal area
Prolonged sitting in wet clothing like swimsuits

The Role of Probiotics

Some research has investigated whether probiotics containing Lactobacillus strains could prevent or treat BV. Results are mixed:

Some studies show benefits from specific Lactobacillus strains
Others show no significant effect
The optimal strains, doses, and delivery methods aren’t established
Probiotics are generally safe but aren’t yet standard prevention

This remains an area of active research but isn’t yet recommended as standard prevention strategy.

What Happens If BV Is Untreated During Pregnancy

Understanding the potential consequences of untreated BV helps put the condition in perspective.

The Absolute Risk of Complications

While BV increases the risk of complications like preterm birth, it’s important to understand absolute risk. Not every woman with untreated BV experiences complications:

Most women with BV deliver healthy babies at term
The increased risk is real but preterm birth rates remain under 25% even with BV
Many factors beyond BV influence pregnancy outcomes
Individual risk depends on multiple factors including BV severity, other risk factors, and prior pregnancy history

This doesn’t minimize BV’s importance, but provides realistic perspective.

Factors Affecting Whether Complications Occur

The likelihood of BV causing problems varies based on:

Severity and persistence of the bacterial imbalance
How early in pregnancy BV develops
Presence of other infections or inflammatory conditions
Prior preterm birth history
Adequacy of prenatal care
Other risk factors for preterm birth
Individual inflammatory responses

Why Treatment Matters Despite Uncertainty

Even though treatment doesn’t guarantee prevention of complications, several reasons support treating BV:

Treatment relieves symptoms when present
It reduces risk even if it doesn’t eliminate it completely
Untreated BV can worsen over time
Post-delivery infection risk is reduced
Treatment is generally safe with minimal side effects

The Limitations of What We Know

Research hasn’t definitively answered all questions about BV and pregnancy. Uncertainties include:

Why some women with BV have complications while others don’t
Whether timing of treatment affects outcomes
What role the microbiome plays beyond BV bacteria
Whether treatment that eliminates BV but doesn’t restore normal flora provides full benefit

These gaps in knowledge explain why screening and treatment recommendations continue evolving.

When to Contact Your Healthcare Provider About Vaginal Symptoms

Knowing when vaginal symptoms warrant medical attention helps ensure timely diagnosis and treatment.

Symptoms That Require Evaluation During Pregnancy

Contact your healthcare provider if you experience:

Any unusual vaginal discharge, particularly if it has an odor or color change
Persistent vaginal itching or irritation
Burning during urination
Vaginal pain or discomfort
Bleeding or spotting along with discharge
Any symptoms that concern you even if they seem minor

Don’t feel embarrassed about reporting vaginal symptoms. They’re common pregnancy concerns that providers address routinely.

Distinguishing Normal Pregnancy Changes From Infection

Pregnancy causes normal changes in vaginal discharge. Typical pregnancy discharge is:

Clear or milky white
Thin and watery or slightly thicker
Odorless or with a mild, non-offensive odor
Present in moderate amounts

Abnormal discharge suggesting possible infection is:

Gray, green, or yellow in color
Accompanied by a strong, fishy, or foul odor
Associated with itching, burning, or irritation
Significantly heavier than your normal discharge

When in doubt, have symptoms evaluated rather than assuming they’re normal.

Why Early Evaluation Matters

Prompt evaluation of vaginal symptoms during pregnancy is important because:

Early treatment of infections like BV may reduce complication risks
Some infections worsen if left untreated
Proper diagnosis ensures appropriate treatment
Vaginal infections can indicate other issues requiring evaluation

What to Expect During Evaluation

When you report vaginal symptoms, evaluation typically includes:

Discussion of symptoms, their onset, and characteristics
Pelvic examination
Collection of vaginal fluid for pH testing and microscopy
Sometimes additional testing for other infections
Discussion of results and treatment if needed

The evaluation is straightforward and provides clarity about whether treatment is needed.

Moving Forward With Knowledge and Appropriate Care

Bacterial vaginosis represents one of those pregnancy complications where the medical evidence is clear in some areas and uncertain in others. We know definitively that BV is common, affecting 10% to 30% of pregnant women, and that it approximately doubles the risk of preterm birth, with rates of 22.7% in women with BV compared to 6.2% without it. We know that symptomatic BV should be treated and that women with prior preterm births may benefit from screening and treatment even without symptoms.

What remains less certain is whether treating all asymptomatic women would improve outcomes, why some women with BV experience complications while others don’t, and exactly how treatment prevents problems when it does work. These uncertainties explain why screening recommendations focus on high-risk women rather than all pregnant women, and why treatment decisions require individualized assessment balancing potential benefits against intervention risks and costs.

For pregnant women, the practical takeaway is straightforward: report any unusual vaginal discharge, odor, or discomfort to your healthcare provider for evaluation. If you’ve had a previous preterm birth, discuss whether BV screening makes sense in your current pregnancy. If BV is diagnosed, understand that treatment is recommended for symptoms or high-risk situations, and that completing the full antibiotic course gives the best chance of clearing the infection. While BV creates real risks, most women with the condition deliver healthy babies at term, and appropriate management reduces those risks further.

Bacterial Vaginosis During Pregnancy