They said gene variants in the mother and fetus can make them susceptible to an inflammatory response to infections inside the uterus, raising the risk that a baby will be born early -- before 37 weeks of gestation.
A preterm baby has a 120 times greater risk of death than a baby born full term, and survivors are at risk of breathing difficulties, bleeding into the brain, and having a significant neurological handicap such as cerebral palsy.
Preterm birth costs the United States $26 billion per year. It is one of the most serious and significant challenges to medicine and society and one whose importance is not fully recognized, said Dr. Roberto Romero of the National Institutes of Health, who presented his findings at a meeting of the Society for Material-Fetal Medicine in Chicago.
Romero said the findings support the notion that preterm delivery is an evolutionary mechanism intended to protect baby and mother from infection.
We have established that one of every three premature babies is born to a mother who has an intra-amniotic infection, an infection in the normally sterile amniotic fluid that surrounds the developing fetus, Romero said.
Because the response to infections is controlled by genes, Romero and colleagues set out to identify which are most likely to play a role in response to infections in the amniotic fluid.
HOPING FOR A DNA TEST
For the study, the team analyzed 190 genes and more than 700 DNA variants from 229 women and 179 premature infants in Chile. They compared these to genes from 600 women who delivered their babies full term.
What we found was there were some DNA variants in the fetus that were associated with the occurrence of premature labor and delivery, and there were some genes in the mother that also increase the risk of premature labor and delivery, Romero said in a telephone interview.
In the fetus, the strongest gene influence was the interleukin 6 receptor, which is involved in the body's response to inflammation.
In the mother, the team focused on one gene called tissue inhibitor of metalloproteinase 2, or TIMP2, which affects structures in the cervix and uterus that get broken down at the start of labor.
Romero said when there is an infection, the combination of these two genetic profiles raises the risk of preterm labor as the body attempts to preserve the mother's and baby's lives.
The hope is that the findings may lead to genetic tests that assess whether a woman is predisposed to premature labor, he said. We are not there, but this is the beginning.
About 500,000 U.S. babies and 13 million babies worldwide are born prematurely each year.