Feb. 7, 2000 GAINESVILLE, Fla.---When the protective, balloon-like membranes surrounding the fetus rupture weeks before the official due date, the fetus is threatened. Its lungs may be too immature to sustain life after birth, but staying in the womb puts it and its mother at risk of infection.
Results from a new University of Florida study may help physicians determine whether an immediate delivery is the best course of action for the 130,000 women in the United States whose pregnancies are complicated by preterm premature rupture of the membranes each year. Such ruptures, which at times appear to be triggered by infection, are linked to at least one-third of preterm births.
The research findings, to be presented Saturday (2/5/00) at the Society for Maternal-Fetal Medicine's national meeting in Miami, show that a test manufactured by Abbott Laboratories accurately determines lung development from vaginally collected amniotic fluid.
The vaginal collection method prevents the need for collecting the fluid via amniocentesis, a procedure in which a needle is inserted through the abdominal wall into the uterus. Besides costing nearly four times as much as the vaginal method, an amniocentesis carries a small risk of infection. It also is a more complicated procedure in patients with ruptured membranes; because there is less fluid than normal inside the uterus, the target for the needle is smaller-increasing somewhat the risk of fetal injury.
The UF study evaluated the TDx/TDxFLx Fetal Lung Maturity II test, which measures the level of phospholipids, a type of fatty acid that increases as the lungs mature.
While fetal lung maturity tests have been available for more than 20 years, until now little research has been conducted to validate the use of this specific test on vaginally collected amniotic fluid.
"This specific test has been used for more than five years, but there has been some ongoing concern that it might not be reliable when used on vaginally collected specimens," said researcher Rodney Edwards, a postdoctoral associate in the UF College of Medicine's department of obstetrics and gynecology. "The fear had been that vaginal discharge, bacteria and mucus would interfere with obtaining an accurate measure of lung development. But we found this was not a problem at all."
In cases of preterm premature rupture of the membrane, lung maturity tests can help physicians decide whether to deliver babies who are past 32 weeks' gestation. A full-term pregnancy is considered 37 to 42 weeks.
To determine whether the TDx/TDxFLx Fetal Lung Maturity II test was accurate when used with vaginally collected samples, researchers reviewed the files of 153 patients treated at Shands at UF between January 1995 and June 1999. They found that in 98 percent of the cases in which the test had indicated mature lung development, the baby had no sign of respiratory distress after delivery. When the test indicated "borderline" lung development, 93 percent of the babies suffered no respiratory problems after birth.
UF researchers concluded that a mature or borderline test result provides a strong indicator that delivery risks only a small chance of newborn respiratory complications.
"It has been demonstrated by other researchers that if a patient with ruptured membranes is between 32 and 36 weeks' gestation and tests indicate mature fetal lungs, the outcome of both mother and baby will be improved with immediate delivery rather than waiting for labor," Edwards said. "With this more active management, infections are less likely for both mother and baby, hospitalization is shorter for the mother and the newborn's length of hospital stay is not prolonged."
Dr. William Herbert, chair of the University of Virginia's obstetrics and gynecology department, said the study was important because many patients come to the hospital with ruptured fetal membranes weeks before their due date.
"This test will be helpful in deciding the best management of these women and their children," he said.
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