Increased Risk of Preterm Labor May Be Linked to Presence of Common Bacterium in Amniotic Fluid, Weill Cornell Study Shows

11% of Women Studied Had Microbe Present Of Those, 59% Had Preterm Labor

Feb 12, 2003

New York, NY

A scientist at Weill Cornell Medical College has discovered that the presence of the microorganism Ureaplasma urealyticum in the amniotic fluid was linked with an increased risk of preterm labor. Results from the National Institutes of Health (NIH)-funded study are published in the current issue of the Journal of Infectious Diseases.

The study found that Ureaplasma urealyticum was present in the amniotic fluid of 11.4 percent of the 254 enrolled women, all of whom were healthy and in their second trimester of pregnancy. Of the women who tested positive for the microbe, 58.6 percent went on to have preterm labor, compared to 4.4 percent of women who tested negative. Additionally, women who tested positive for the microbe had a higher prevalence of preterm labor in a prior pregnancy (20.7 percent versus 2.7 percent); this suggests that the microbe may be present in the uterus even prior to conception.

It remains undetermined whether Ureaplasma directly causes preterm birth, or if it is a marker for another infection, said lead author Dr. Steven S. Witkin, Professor of Immunology in Obstetrics and Gynecology at Weill Cornell Medical College. Nevertheless, identification of this microorganism in second trimester amniotic fluids identifies pregnant women at increased risk for a preterm birth.

The test, which employs a DNA amplification technique called polymerase chain reaction (PCR), can also be performed prior to conception on a sample obtained from the uterus. PCR has been established as a superior method to the traditional culture testing method.

Preterm, or premature, birth occurs in about 10 percent of all pregnant women and is the most common cause of neonatal deaths in the U.S. The largest risk factor for preterm birth is a prior preterm birth. The leading causes of preterm birth are infection, placental pathology, maternal stress, and incompetent cervix.

According to Dr. Witkin, there was no relationship between the presence of the microbe and the age of the patient or number of previous pregnancies or births. The extent of Ureaplasma colonization is known to vary among ethnic groups. The study's enrolled population consisted of 254 asymptomatic pregnant women of Swiss origin at 15-17 weeks' gestation.

Ureaplasma urealyticum frequently colonizes the lower genital tract of pregnant women, without adverse consequences. However, in a small group of women, the microorganism ascends and colonizes the lining of the uterus, either before or after conception.

Further research is needed to determine why preterm birth occurs in some women but not in others who test positive for Ureaplasma and to examine whether antibiotic treatment will improve pregnancy outcomes for women whose second trimester amniotic fluid tests positive.

Additional study authors include Dr. Stefan Gerber, Dr. Yvan Vial, and Dr. Patrick Hohlfeld of Centre Hospitalier Universitaire, Vaudois, Lausanne, Switzerland. Dr. Gerber was a Fellow in Dr. Witkin's laboratory at the time of this investigation.