The study analyzed 5,762,037 live births and 11,897 infant deaths in the United States between 1998 and 2001. Among the sample were 311,927 low-risk women who delivered through Caesarean section, a trend that has increased from 20.7 percent in 1996 to 29.1 percent in 2004, according to the report.
The primary cause of death -- regardless of delivery method -- was congenital malformations, but when that cause of death was excluded from the calculation, the risk of death in Caesarean section deliveries was still high. The researchers also found that eliminating death by intrauterine hypoxia, or lack of oxygen -- often a reason for performing a Caesarean section -- still left the Caesarean section mortality rate at more than twice that of vaginal delivery.
The researchers theorized that the increased mortality rate may be partly due to the fact that labor releases hormones in the baby that promote healthy lung function, and the compression of the baby's body during labor can help expel fluid from the lungs and prepare them to breathe air. Also, Caesarean sections' inherent risks -- such as possible cuts to the baby during the procedure or delays in breastfeeding -- were named as possible contributors to the increased death rate.
"Neonatal deaths are rare for low-risk women -- on the order of about one death per 1,000 live births -- but even after we adjusted for socioeconomic and medical risk factors, the difference persisted," said lead study author Marian F. MacDorman, a statistician with the U.S. Centers for Disease Control and Prevention. "This is nothing to get people really alarmed, but it is of concern given that we're seeing a rapid increase in Caesarean births to women with no risks," she said.
While the over 5 million birth study sample was considered large enough to draw conclusions that were statistically significant despite the rarity of neonatal death, the authors noted that there was no way to confirm certain factors, such as the accuracy of the medical information on birth certificates. The birth certificates provide accurate information on delivery methods and birth weight, but the researchers were concerned that they may underreport individual medical risk factors. They concluded that the Caesarean section group in their study could have been at an inherently higher risk, but added that was unlikely.
Dr. Michael H. Malloy, study co-author and professor of pediatrics at the University of Texas Medical Branch at Galveston, said that the findings of the study should be considered when doctors are advising their patients on delivery methods.