MONDAY, Jan. 28, 2002 (HealthDayNews) -- Pregnant women may want to think twice before taking antibiotics during their second trimester of pregnancy.
That's the finding of a new University of Alabama study presented last week at the annual meeting of the Society for Maternal-Fetal Medicine in New Orleans.
While the drugs are commonly prescribed to treat vaginal infections that were believed to cause premature labor and early birth, the new study shows the drugs won't help -- and they might even increase the risk of delivering early.
Lead author Dr. John Hauth notes the two most commonly prescribed antibiotics -- metronidazole and azithromycin -- not only failed to prevent early births in two of the three risks groups studied, but "pre-term births were higher in women given the antibiotics."
For obstetrician Dr. Andrei Rebarber, of the New York University Medical Center, the study offers important information doctors can put to immediate use with their patients.
"It seems that research was well-conducted, and it offers some important proof that vaginal infections do not always mean a corresponding infection in the uterus exists. This is something both women and their doctors need to discuss before deciding whether or not medication is necessary," Rebarber says.
The notion that vaginal infections require antibiotics in pregnancy came about because doctors believed certain bacteria present in the vagina could easily ascend into the uterus, where the resulting inflammation could cause pre-term labor and an early delivery.
Often, doctors believed infection in the vagina was a good indicator that a uterine infection was present as well.
However, says Rebarber, this isn't always the case.
"Vaginal infections are not always a marker [warning flag] for uterine infection. And as this study showed us, sometimes treating these infections can cause more problems than if they were left alone," says Rebarber.
Indeed, the study revealed that some women who were treated with antibiotics actually gave birth earlier than those whose infections went untreated.
One possible reason, says Rebarber, is that sometimes in the course of killing one bacteria, an antibiotic can upset the natural balance of organisms in the vagina, setting the stage for an even more virulent germ -- such as E. coli -- to take control.
"If this bacteria ascends into the uterus, there is even a greater chance that the pregnancy can be disrupted and premature labor can result," says Rebarber.
Hauth and his team at University of Alabama at Birmingham looked at 370 women believed to be at high risk for pre-term birth. They included 235 women who tested positive for high vaginal and cervical levels of fetal fibronectin, a chemical marker for premature labor; 60 women with bacterial vaginal infections; and 75 women with vaginal infections and a pre-pregnancy weight of less than 50 kilograms.
The women were randomly selected to receive either a placebo or a combination of 1 gram daily of azithormycian for four days, plus 750 milligrams of the slow-acting antibiotic metronidazole once a day for seven days.
According to Hauth's study, women with elevated fetal fibronectin who took the antibiotics had earlier deliveries than those who took a placebo -- 21.7 percent versus 12.6 percent.
Additionally, women who had all three risks factors -- high fetal fibronectin, a vaginal infection and low weight -- and took the antibiotics had nearly twice the risk of pre-term labor than those who took a placebo -- 24 percent compared to 13.8 percent.
"Clearly, not only was there no benefit for these women in using antibiotics, but the study suggests that in some instances, the women taking the antibiotics fared worse, and ended up delivering even earlier than those who did not get the medication," says Rebarber.
In addition to the short-term negative effects of antibiotics, Rebarber cautions not to forget the broader issue of antibiotic resistance, particularly concerning bacteria that tend to cause vaginal or uterine infections.
"The more we treat these infections unnecessarily, the more resistant the bacteria become, and ultimately the greater the risk for all pregnant woman," says Rebarber.
What To Do: To learn more about screening for vaginal infections in pregnancy, visit The Midwife Archives. To find out more about premature labor, visit the medical library of the American College of Obstetricians and Gynecologists.
