Bacterial vaginosis is described by the American Pregnancy Association as an imbalance of bacteria in the vagina. Inside the vagina is a bacterium known as lactobacilli which helps to fight any harmful bacteria introduced into the vaginal environment. If the numbers of lactobacilli fall too low, this harmful bacteria can begin to grow uncontrolled, leading to bacterial vaginosis. Approximately 20 percent of pregnant women experience bacterial vaginosis during their pregnancy. It must be treated properly and promptly to prevent preterm labor.
Metronidazole is the antibiotic of choice for treatment of bacterial vaginosis in both pregnant and non-pregnant women. A 2002 review in the Oxford Journal states that the cure rate for bacterial vaginosis is 84 to 96 percent when 500mg of metronidazole is given twice a day for seven days. Contrary to past concerns, studies do not show any increase in negative effects to babies whose mothers received the medication during their first trimester.
Clindamycin is a second oral antibiotic which may be prescribed during pregnancy. The American Pregnancy Association notes that 300mg of clindamycin is prescribed to be taken for seven days. This treatment has a success rate of 94 percent. Drugs.com reports that clindamycin can cause stomach upset, including nausea and vomiting. It can also cause diarrhea, throat irritation and a rash.
Both metronidazole and clindamycin may be prescribed for use topically. Metronidazole is prescribed in a strength of 0.75 percent as a vaginal gel. When applied over the course of five days, it has a cure rate of 75 to 81 percent. Clindamycin is prescribed in a strength of 2 percent as a vaginal cream. It is also applied daily for five days, and has a cure rate of 82 to 96 percent. The American Pregnancy Association warns that only treating bacterial vaginosis topically relieves symptoms and treats the condition in the lower genital tract. Bacteria in the upper genital tract may be left unaffected and may still result in preterm labor.