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Analysis of millions of US births shows association between birth defects and preterm birth

May 21, 2008

Babies born preterm were more than twice as likely to have major birth defects as full-term infants, according to a new analysis of nearly 7 million U.S. live births published online this week in the Springer journal Maternal and Child Health Journal.

Preterm birth, live birth before 37 completed weeks gestation, is a growing national health crisis, according to the March of Dimes. More than a half million babies are born too soon each year, and the rate continues to rise. Birth defects and preterm birth are the leading causes of infant death.

About 8 percent of babies born preterm had a birth defect, according to the research by a team of investigators from the March of Dimes, the U.S. Centers for Disease Control and Prevention (CDC), and several other major institutions.

For this study, the researchers looked at live births between 1995 and 2000 from 13 states, representing about 30 percent of all U.S. births. The findings supported those of earlier, smaller studies.

"The causes of most birth defects are still not known," says Margaret Honein, PhD, MPH of the CDC's National Center on Birth Defects and Developmental Disabilities and lead author of the study. "While it is likely that the most common defects are caused by a combination of genetic and environmental factors, the identification of specific risk factors continues to be a major research and public health priority."

Research into the link between birth defects and preterm birth was called for in the PREEMIE Act (P.L. 109-450) that was signed into law in December 2006. The act, which authorized increased federal support for research and education on prematurity, also called for a Surgeon General's Conference, scheduled for June 2008, to establish a public-private agenda on premature birth.

"Infants born preterm were more than twice as likely to have major birth defects as infants born at term, and the association was strongest among very preterm babies," said Joann Petrini, PhD, MPH, director of the March of Dimes Perinatal Data Center, who also co-authored the study. "This study highlights the importance of understanding the possible shared causes and risk factors that lead to preterm birth among those infants affected by major birth defects."

Very preterm babies, those born between 24 and 31 weeks gestation, were five times as likely as full-term infants to have a birth defect. The most common birth defects for this group were central nervous system defects, such as spina bifida, and cardiovascular defects, such as a hole in the heart.

March of Dimes Foundation