The widely-held assumption that a cesarean delivery has no health risks for the baby is being challenged today by new research that found the procedure did not help some preterm babies who were small for gestational age, and may even have contributed to their breathing problems.

The research, presented at the 32nd Annual Society for Maternal-Fetal Medicine Meeting, "The Pregnancy Meeting" showed that small for gestational age babies delivered early by c-section had higher rates of respiratory distress syndrome than similar preterm babies who were born vaginally.

"These findings overturn conventional wisdom that c-sections have few or no risks for the baby and are consistent with the March of Dimes effort to end medically unnecessary deliveries before 39 weeks of pregnancy," said Diane Ashton, MD, MPH, March of Dimes deputy medical director. "Although in many instances, a c-section is medically necessary for the health of the baby or the mother, this research shows that in some cases the surgery may not be beneficial for some infants."

The study, "Method of Delivery and Neonatal Outcomes in Preterm, Small For Gestational Age Infants" is the ninth study by SMFM members to be honored by the March of Dimes for innovative research focused on preventing premature birth and its complications.

Led by Erika F. Werner, MD, MS, assistant professor of Maternal Fetal Medicine at the Johns Hopkins School of Medicine, who performed the work with Heather S. Lipkind, MD, MS, assistant professor of Maternal Fetal Medicine at Yale School of Medicine, the researchers reviewed birth certificate and hospital discharge information for 2,560 small for gestational age babies who were delivered preterm. C-sections often are performed for babies diagnosed with intrauterine growth restriction who are not growing adequately in the womb. Dr. Werner and her team found that small for gestational age babies delivered by a c-section before 34 weeks of pregnancy had a 30 percent higher odds of developing respiratory distress syndrome than babies born vaginally at a similar gestational age.

Research by the March of Dimes and the Centers for Disease Control and Prevention in 2008 found that c-section deliveries accounted for nearly all of the increase in the U.S. singleton preterm birth rate between 1996 and 2004.

Preterm birth, birth before 37 weeks of pregnancy, is a serious health problem that costs the United States more than $26 billion annually, according to a 2006 Institute of Medicine report. It is the leading cause of newborn death, and one million babies worldwide die each year as a result of their early birth. Babies who survive an early birth often face the risk of lifelong health challenges, such as breathing problems, cerebral palsy, learning disabilities and others.

The March of Dimes says that if a pregnancy is healthy and there are no complications that require an early delivery, women should wait until labor begins on its own, or until at least 39 weeks of pregnancy. Many of the baby's important organs, including the brain and lungs, are not completely developed until then.

For more than two years, the March of Dimes has been working with hospitals and health policy experts to implement a tool kit it developed with its partners that promotes policies and practices to reduce the number of medically unnecessary c-sections and inductions scheduled before 39 weeks of pregnancy.

Explore further C-sections a critical factor in preterm birth increase