Bacterial Vaginosis (BV) is a common condition resulting from an imbalance in the vaginal microbiome. The naturally dominant Lactobacillus bacteria decrease, allowing an overgrowth of other anaerobic bacteria. This shift affects up to 30% of pregnant women, though many may not experience noticeable symptoms. While BV is treatable, its presence during pregnancy is associated with certain obstetric complications, requiring discussion with a healthcare provider.
The Link Between BV and Preterm Delivery
The primary concern regarding Bacterial Vaginosis during pregnancy is its established, though indirect, link to an increased risk of preterm delivery, which is defined as birth before 37 weeks of gestation. This complication arises not from direct harm during the birth process itself, but from the effects of the bacterial overgrowth earlier in the pregnancy. BV can increase the risk of preterm birth by approximately 1.5 to 2 times, with some studies suggesting an even higher risk when the infection is present early in gestation.
The mechanism connecting BV to premature birth is rooted in the body’s inflammatory response to the infection. The anaerobic bacteria associated with BV, such as Gardnerella vaginalis and Mycoplasma hominis, produce substances that can ascend from the vagina into the upper genital tract. These bacteria or their byproducts, including proteolytic enzymes, can create a state of chronic inflammation in the uterine environment.
This inflammation can lead to the weakening of the amniotic membranes and the cervix, which increases the likelihood of premature rupture of membranes (PROM). The presence of these pathogenic bacteria can also trigger the release of inflammatory signaling molecules, called cytokines, which may initiate uterine contractions prematurely. Therefore, the risk associated with BV is primarily a risk of the pregnancy ending early, before the baby is ready for delivery.
Due to this association, the Centers for Disease Control and Prevention (CDC) supports screening and treating all pregnant women who display symptoms of BV. For asymptomatic pregnant women, most organizations, including the American College of Obstetricians and Gynecologists (ACOG), do not recommend routine screening. However, the CDC and ACOG suggest screening and treating asymptomatic women who have a history of previous preterm delivery, as they are considered high-risk.
Potential Neonatal Complications from Exposure
The direct harm to a baby during delivery from maternal BV is related to the infant’s exposure to the high concentration of pathogenic bacteria in the birth canal. The baby can acquire the BV-associated bacteria as they pass through the vagina. A baby’s exposure to these bacteria can contribute to specific, though rare, neonatal infections.
Studies have shown that exposure to BV, even in infants born at full-term, is associated with a higher risk of certain adverse outcomes. These include an increased need for assisted ventilation or respiratory distress at birth, and a higher rate of admission to the neonatal intensive care unit (NICU). There is also a notably increased risk of neonatal sepsis, which is a bloodstream infection in the newborn. The risk of neonatal sepsis for full-term infants exposed to BV has been estimated to be 1.6 times higher than for unexposed infants.
For infants born prematurely, a consequence often linked to BV, the risks are compounded. Preterm delivery often results in a lower birth weight, which is an independent factor that exacerbates the severity of any potential neonatal infection or respiratory issue. Exposure to BV can also be associated with meconium staining at delivery, which is a sign of fetal distress in the uterus. Pediatricians monitor exposed newborns closely for signs of infection, such as respiratory distress syndrome, especially if the mother was known to have BV at the time of birth.
Screening, Diagnosis, and Treatment Options
A diagnosis of BV during pregnancy is made using several clinical methods. The initial evaluation often involves assessing symptoms, such as the presence of thin, gray or white vaginal discharge and a strong, fishy odor. A healthcare provider will test the vaginal discharge, which often shows a vaginal pH level of 4.5 or higher, indicating the loss of the normal, protective acidity.
The diagnosis is further confirmed through a microscopic examination of the vaginal fluid, known as a wet mount, to look for “clue cells,” which are vaginal cells coated with bacteria. The gold standard for laboratory diagnosis is the Nugent score, a grading system based on the types and numbers of bacteria seen on a Gram stain. For pregnant women with symptoms, treatment is always recommended because of the associated adverse pregnancy outcomes.
The standard treatment involves prescription antibiotics, which may be given orally or applied as a gel or cream directly into the vagina. Oral medications like metronidazole and clindamycin are commonly prescribed and are considered safe for the baby during pregnancy. For high-risk pregnant individuals, such as those with a history of preterm birth, systemic oral treatment is often preferred, as it may be more effective in reducing the risk of a future preterm delivery compared to topical treatments. Adherence to the full course of antibiotics is important to eradicate the infection and reduce the chance of recurrence.